If you want hacked firmware, dont update. Else its a good update.. Better sound quality, better battery life, better auto rotation etc.
if u hack ur firmware first and then update then the hacks work fine .. i did not find much improvement in sound quality with ver 30 firmware though. may be battery life improved ..though i dont agree with auto screen rotation ..it took more time to rotate than ver 20 firmware .. n85 is far better in that aspect..screen rotation is pretty fast. I like it that way ..