It is from Players Handbook 2, and it Alters Game Balance! (Quick description)
As a more detailed description: +1 Bonus to Attack at lvls 5/15/25 (I.e. +3 at lvl 25)
Q&A
Do people exclude it from their games: No, they just whine (Like me)
Is it imbalanced: YEs, Must have feat.
Enjoy