i thought i heard that you can still do over the air updates, but then your root access is gone until the experts figure out how to root it on the newer version. i could be wrong. this is my first time rooting. it wasn't this difficult with BB as far as getting hybrid OS builds, so I am not too sure how it all works on android phones.
voiding warranty, i have heard the same thing, how it is voided afterwards. what i don't understand, if you put a new software revision on your phone, how can someone tell you rooted it once before? i'm guessing there is some permanent firmware change once you root your phone.