Z4Root was never updated after Froyo. NG for GB.
Yes, rooting breaks the warranty. But you have the option of reverting back to stock (if you learn how) if you ever need a warranty replacement for a hardware issue.
Don't know if there's a no-root fix or not.
For more info on rooting, etc, check out QBKing's how-to videos:
[ACS] [HOW TO] Root, Flash Roms/Kernels/Themes, CWM, and update! (67 videos) 8/7/11 - xda-developers