My group was discussing some changes to the Aid Another ability. At low levels, that +2 might be significant. At high levels, that +2 isn't going to help a non-specialized character succeed on the relevant check. So we decided that Aid Another should scale somehow, either by level or by success on the relevant check.
Here are our two options.
Option 1
The base check for Aid Another is DC10, this provides the basic +2 bonus. For every 5 points that the ally exceeds that check, she offers another +1 bonus (+3 for DC15, +4 for DC20, etc.) The player rolling for the Aid uses her full skill bonus for this roll. Only one ally can Aid Another for any relevant check and the DM has the right to rule that Aid Another cannot be used for a particular skill or for a particular use of a skill.
Option 2
The base check for Aid Another is DC10, this provides the basic +2 bonus. For every 4 skill points a character has in the relevant skill, the Aid Another bonus increases by 1. The player rolling for the Aid does not apply any skill bonus to the roll. He rolls a D20 and succeeds on a 10 or greater. Only one ally can Aid Another for any relevant check and the DM has the right to rule that Aid Another cannot be used for a particular skill or for a particular use of a skill.
I am thinking that Option 1 needs some sort of hard cap on the bonus that can be offered, but I couldn't think of a reasonable one. What do you think?
The Complete Adventurer (I think) had a rule like your option one. The increment was ten instead of five, though. It's the one my groups always use.
The main place this becomes an issue is with opposed checks at higher levels. Really, though, we implemented it because it sucks to be the guy rolling 35 on aid another checks and doing no better than the guy making 10.
Stealth, mostly. Our group is very polarized on the skill, either they have ridiculous specialization in it, or they are like me and have a penalty in it. Having the ranger (highest stealth bonus) aid the cleric and fighter in hiding is almost useless since currently he can only offer a +2.
The houserule would mostly be there to help those that aren't proficient in a certain skill have a chance of succeeding.
Ok, found my copy of the Complete Adventurer. They offer two optional rules that you might want to use. First,
When a character with 5 or more ranks in a skill uses the aid another action to assist another character's skill check, he can grant a higher bonus... For every 10 points of the helper's check result above 10, the circumstance bonus increases by one.
Second,
A character with 5 or more ranks in a skill who is engaged in a task using that skill can voluntarily accept a -4 penalty on the check in order to grant a +2 circumstance bonus on the same skill checks made by nearby allies engaged in the same task.
Hope these help.
We generally keep the +2, but we do allow additional people to help if they have at least 5 ranks in the skill (or relevant skill). For every doubling of the number of people you get another +2.
This usually only is used for things like setting up a defensive position and setting traps (IE: The person with the highest Knowledge (Tactics) or Knowledge (Engineering) or Knowledge (Geography) depending on what type of defensive position you are setting up is the primary. Anyone that can reasonably contribute (craft (trapmaking), survival, same knowledge, etc, makes an aid another. Then the main person adds in all extra +2's and makes a check. That's the check for their defensive position. I use that to determine how to play the bad-guys when they attack, if they do).
We added Knowledge (Tactics) as a skill, and someone with it can make an 'Aid Another' action to give a +2 to initiative in combat. They can also use it for setting up defensive lines, etc. I then adapt the enemies based on how well they make their roll. Since the players are not as good as the characters at tactics, I 'dumb down' the enemies if they make a really good tactics roll. If they flub it big time, I play them extra aggressive/smart or give them a boost in hit-points to make them harder.
EDIT: Of course, no matter how good a tactics roll they make, it doesn't help them with fubars they make themselves, like the time the Centaur charged up to a stream as 7 bugbears came racing forward to attack the party. The fully armored duerger duskblade made his reflex save when dropped and didn't roll into the stream.
The fully armored kobold marshal (wearing adamantine no less) horribly failed his and rolled forward into the 2 foot deep stream, and didn't have the strength to pull himself out. To add insult to injury, the druid's entangle pinned him to the bottom of the stream. Then the bugbears rubbed salt in the wound by stepping on him and using him as a stepping stone. The scout dropped out of the fight because he couldn't keep attacking he was laughing so hard when the first bugbear died and fell on top of the kobold. He actually passed out from lack of oxygen (the scout, not the kobold) when the second bugbear fell on top of the first.
They managed to get the kobold out before he died from drowning/suffocation, but it was a near thing.