Yeah, we brought in a couple of new PCs after a death and they were both bearing the mantle of the Red Rider. Since they came in at different times, the story was that they each thought the other one had died and that they were the last one left from their previous party. Imagine their surprise when they found each other. They had an awesome "bro-ment" together upon reuniting, made more awesome by the fact that those two characters, both male, are played by the two women in our group.
The Heretic Tangent101 subversively, and clearly under the influence of Chaos wrote:
Have to wonder if the Imperials would have declared Exterminatus on Golarion...
The world formerly known as Golarion has, in His eternal wisdom, been declared Exterminatus by His Imperial Majesty. The Chaos portal colloquially known as the "Worldwound" has existed for far too long for the populace of that world to be anything but a liability to the Imperium of Man. Once the world has been cleansed of all life, the highest priests of the Imperium will descend upon the glassy orb to close off the violent warp energies spewing forth from the unholy breach.
Citizen Tangent101, for the crime of speculating that said world might be redeemable, your sentence is Execution. One weak mind can doom an entire world, and His Imperial Majesty's will is clear here. Before your heresy of speculation can spread throughout the Empire, He will make an example of you before the massed people of your Hive.
You are truly blessed in this moment, that you have been chosen to teach an entire world the consequences of weakness and heresy.
Long live the Emperor!
I agree with most of what's been said here. Traps by themselves are awful, and "keeping players on their toes" just makes your games take forever. I'm playing the trap guy in one game right now, and it's basically just "we search the room and disable the traps". There's no real interaction, but adding that "mandatory" step to everything slows everything down.
In set pieces, however, I use traps all the time. Pits are wonderful tools for encounter design, as are giant gouts of flame that go off every other round, or collapsing ceilings. Those are all things the PCs and NPCs can interact with in interesting ways. The NPC positions himself precisely so that the flames go off around him and cook the fighter, or the cleric gets bull rushed into the pit - wonderful stuff. One of my favorites is to have kobolds run away down a hallway full of traps set to go off when medium creatures step on them.
The key with traps is to make them interesting and interactive, rather than an "action tax".
You seem to have taken the advice from the other posters constructively, for which I want to thank you. The KM boards are my favorite place on the whole Paizo forums*.
So, if I understand you correctly, you are saying that the reason why Nyrissa doesn't kill the PCs while they are weak is because "the story demands it".
The moment you look at a CR 20 BBEG and ask why she hasn't wiped the APL 4 party off the map given that she appears to have the motive, method, and opportunity is the moment you have to begin to look at a couple of important factors.
Firstly, if you were her (or if your PCs were APL 20 demigods), what would you do about some jerks who built a castle in the Greenbelt? If the answer is "Wipe them out by showing up on a Jabberwock with my dragon pal" then ask yourself a follow-up question- how would I feel if my DM did that to me? It also turns into a very different game at that point, because either the PCs are all dead and the new party is off on a quest to find Briar and level up enough to go get her, or they escape and do the same. Either way, it's not really Kingmaker anymore.
Secondly, if you don't like the answer you get from the first question, you then have to figure out a way to get an answer you do like. Orthos decided that she didn't have the ability to get to the Stolen Lands in the first place. Caleb has argued that she doesn't really have the motive to come down here in person to deal with ants. Basically, one of the premises must be false, otherwise she would have killed all the PCs by now.
You're a Kingmaker DM, which means you get to make some really cool decisions about how the campaign works, who wants what, and why - and most importantly, you get to help your friends build an awesome kingdom from the ground up. Instead of implying that "the story demands it" is a cop out, think about why your fellows are sitting there asking you to help them feel like heroes for a few hours a week.
Just an aside, the Kingmaker DMs and players on here are some of the most civil, well-informed, creative, and dedicated people I've had the fortune to meet playing this game. Most of the time, I wish I could just post my non-KM stuff here instead of the proper forum, and I'd love to buy many of you a drink (alcoholic, caffeinated, or simply refreshing, whichever you prefer) if I ran into you IRL.
There are a ton of really good suggestions on this thread. I've been running games primarily for optimizers and powergamers for seven or eight years now, and basically everything up there has happened in my games somewhere. If you look closely, you'll see that most of the advice here boils down to "make them make hard decisions".
When a game is on "easy mode", you can end up with a situation where the "conflicts" are simply set dressing for your players to show off how awesome they are. That's fine, and since my players are pretty awesome, I like them to be able to show off. However, years of running Exalted back before I picked up 3.5/PF/4e taught me that you can make a game REALLY challenging by assuming your PCs will succeed at anything they try.
It sounds counterintuitive, but the way it works is that you always bring back the repercussions of what they've done. Pathfinder, like Exalted, always has someone bigger than the PCs out there that likely doesn't much care for having their plans interrupted. Make sure that there's always at least a couple of those people. That'll do a couple of things. First, it'll mean that if they kill/defeat/enslave/convert one, the rest are still out there. Second, it'll mean there's more bad stuff happening than they can deal with right now.
First level example:
The local goblins have cut off the main trade route into the village, your sister and her friends have gone missing while exploring the abandoned mine, and the Mayor came back from the capital with a strange new advisor.
Fifth level example:
An orc army is marching on the Barony the PCs live in, spies from the kingdom next door (that has always coveted the rich lands/mines/ley lines/whatever) have infiltrated the government/military/church, and that glowing sword you picked up is giving the paladin stronger and stronger visions.
Tenth level example:
A reborn madman from ages past has awakened an ancient evil relic, but the King is in a coma after being attacked by unknown assassins, and a pair of dragons has taken over the main trade route.
Fifteenth level example:
Karzoug, Tar-Baphon, and Nyrissa. Aaaand GO!
What this does is force them to make the hard decision to prioritize one thing over another. I assume that because they're really good at what they do, that they could easily deal with one of those things at a time, and two wouldn't really be too tough either, but if all three are going at once, it's much more difficult. They'll still be able to fix whichever problem they choose to focus on, but the trick then becomes how they choose to mitigate the fallout from possibly doing the other two less well than they had hoped.
At the level of encounter design, it works the same way. A larger number of relatively small monsters produces the same effect, but on a battlefield scale, especially if you use a variety of monsters. 4e was really good at this with their monster roles, but basically make sure that not all the monsters are attacking the same place, the same way, at the same time, and you're in great shape.
It might begin to stretch credulity for some people (how come bad stuff keeps happening at the same time as all the other bad stuff?!) but the way I see it, you didn't sit down to play a random slice of time with a random group of characters. You sat down to play the most interesting time in the lives of the most interesting people on Golarion. (Hint: your players' characters are ALWAYS the most interesting characters in the world you're playing in.) Make that true however you need to.