Now, I'll preface this with the disclaimer that most of the time, not all the time but most, I play using the default Pathfinder Campaign Setting with most of the differences being due to the actions my player's have taken, with a few changes of my own (i.e. Lissala is Lawful Neutral, not Evil) but still, sometimes you just want to run a campaign that wouldn't work in Golarion as written, and you don't feel like making sweeping changes to the setting to make room for one campaign.
Still, even after you've constructed a new world in which your party of half-dwarves, psionic fishpeople, and valiant hobgoblins can successfully crusade against the insane machinations of the Twice-dead armies of the Gnomish Confederacy, there is still room for some things from Golarion proper to fill out the rough edges. After all, in the immortal words of Pablo Picasso "good artists borrow, but great artists steal."
Since I started the thread, I'll answer my own question first. A while ago I was running a homebrew campaign where all the continents had been shattered in an ancient cataclysm, creating a planet consisting of rough seas and vast archipelagos. It worked well for the type of game I was planning (a very episodic, Star Trek-esque new culture and threat every week sort of thing) but I felt like it needed an overarching threat to make it so my players would feel like they were actually accomplishing something other than killing things and taking their stuff. While I was debating what might be a good choice for the task, seeing as it would have to be a monster that was moderately powerful, had a good connection flavorwise, and wasn't such an obvious choice that anyone would be able to figure it out before I had a chance to properly set it up (e.g. "Oh we're in *not*-Egypt? I'm sure the villain is totally not a mummy!") my eyes caught upon one of the modules on my shelf, and after that, the choice was obvious.
You see, I happened to see one of the best Pathfinder modules there is (at least in terms of setting), that is to say The Moonscar and if you're anything like me, all you need to here about it is the phrase "Jungle Moon Succubi" and you're hooked. If you're a DM and that combination of words doesn't leave you proverbially salivating at the very thought of such a thing ...that is in entirely fine as no two tables are going to be exactly the same, and everyone gets something different out of this game, but for me that was the coolest thing since sliced bread. The Campaign practically wrote itself, with the PC's fighting islands whose leaders were dominated or charmed by succubi, lead by tieflings or half-fiends descended from the aforementioned succubi, or who worshipped the succubi as dark goddesses. Even when my players did fight succubi or other demons, they had no inclination that they we were popping in from the Moon of all places until very late into campaign and even then only after hints being dropped since level one.
All in all, it was one of my most successful homebrew campaigns, and it all started due to me blatantly stealing from another campaign setting.
Now, after I've spent the last couple paragraphs of this post boring you with personal anecdotes, back to the question at hand. What things from Golarion have you mixed in to your home settings?
Offhand, all I can think of are the Red Mantis Assassins. I'm sure there are several small tidbits here and there but they don't come to mind now.
I've taken the idea of a once-great nation shattered by a nearly world-ending cataclysm. In my game, as opposed to a human empire destroyed by abolths, it was an empire largely ruled by and composed of dragons and other dragonoids that was destroyed by the first human empire, jealous of the might and resplendance of the dragons.
I use Mystara geography and country overview and update it with Pathfinder. Certain countries match up quite nicely. For example Ustalav and Karameikos. They have that Curse and Tarot thing going on!