I tend to keep my house rules minimal. About the only real game-changer I had for 3e was that I gave feats every odd level instead of every 3rd level, with an extra at level 1. I also combined Listen/Spot into Perception, Hide/Move Silently into Sneak, and Balance/Tumble into Acrobatics.
My main goal was that I wanted to make sure I could use HeroForge for character generation. bonus feats were easy, and - remarkably - the skill combinations were pretty simple, too.
So far, I have zero house rules for 4e. It's very new, and I feel a great freedom to hand-wave stuff like a horse's carrying capacity. I am keeping up with errata, though.
-O