Multiple Tiny Bonuses:
I don't want to deal with a bunch of +1 bonuses. e.g. the dragonborn ranger (hunter) that gets +1 if I'm bloodied, +1 if the enemy is alone, +1 if an ally is adjacent to the enemy, +1 if I'm the closest to the enemy, +2 if I have Combat Advantage, -2 if it's dim light, etc.
If a bonus that I get for during combat isn't at least +3, don't bother. Out of combat, if it's more of a static bonus (+1 sword), then I can write it down on my character sheet and factor it into the numbers there.
A possible solution would be to just give me a power that I can use only 1/encounter to add +3 with the same requirement as before.
For a more out-there solution, say the first type of situational bonus from any source gives me +3, the next bonus an additional +2, the third bonus an extra +1, and any other bonuses don't have an effect. If you need more than a situational +6 bonus, you're probably way out of your league or you're slowing down the game doing all that counting of modifiers..
The problem with dynamic bonuses above +1 or +2 is that it is too easy to get multiple ones and then activities become nearly automatic.
So I wouldn't mind a +3 dynamic bonus, as long as it doesn't stack with any other in combat bonuses. And, as long as the PC didn't have a lot of ways to get static bonuses on the character sheet.
The game system either has to have a lot of stackable little bonuses, or it has to have a few non-stackable larger bonuses.
And a +6 dynamic bonus on a D20 should be out of the question. +3 is about as high as it should get.