[MENTION=996]Tony Vargas[/MENTION], plus anyone else who is following along:
One of the PCs in my game is an invoker with wizard multi-class. His Paragon Path is Divine Philosopher, and as an Epic Destiny he is intending to take Sage of Ages. His feats include two skill-training feats, plus a power swap feat to get the wizard utility Arcane Gate.
Sage of Ages has the following 26th level Utility:
Trick of Knowledge
Encounter * Arcane
Minor Action, Personal
Effect: You make an Arcana check and gain a benefit based on your check result until the end of the encounter.
30 or lower: No effect
31-35: +5 bonus to saving throws
36-40: + 2 bonus to all defenses
41-45: + 2 bonus to attack rolls with arcane powers
46-50: Make saving throws at the start of your turn instead of the end of your turn
51-55: Pick two benefits you can gain from a roll of 31 through 50
56-60: Pick three benefits you can gain from a roll of 31 through 50
61 or higher: Gain all four benefits you can gain from a roll of 31 through 50
I don't know if the player has noticed yet that, as written, the only benefit the "41-45" result of this power will give will be to his encounter use of Thunderwave (from his multi-class feat). I am intending, in due course (ie when it actually matters, in 8 levels time), to allow the +2 bonus to attack to apply to all the PCs' attack powers, both Thunderwave plus his divine attack powers.
That is a modest house rule. At my table we use quite a few house rules like that (eg another one governs the interaction between power sources for a fighter-cleric-paragon warpriest). They're not hard to implement!, and are not going to break their game. Their impact on play is obvious and deliberate.
We have other house rules too, like an agreement on how dazing mid-turn works (if you get dazed mid-turn, you lose the rest of your actions; if you get undazed mid-turn, you get back the rest of your action - for the first year or two we ran it the other way, but didn't like how it played). And two of our house rules - that weapon focus etc don't help sorcerer dagger implement attacks, and that bonus saves can't make you worse off if you failed them - have since been made an official rule (official errata, and stealth errata in Essentials respectively, I think).
Plus there's my (weaker) version of [MENTION=87792]Neonchameleon[/MENTION]'s "extended rest" rule (ie in contexts of hard wilderness or underground travel, making extended rests a function of more than just the passage of time).
Outside of the context of organised play, which obviously has its own logic, is there anyone who's not doing this sort of thing in their 4e game - tweaking here and there to make the game better fit the PCs their players are trying to build, and the dynamics of play as they're experiencing them at their tables?