I'm no expert on this, but probably the best answers are "If it ain't broke, don't fix it" and "No need to hurry". The newest iOS update is v4.3.2, but I haven't installed it yet. I'm waiting to see what people say about it; so far, I haven't seen any reports of problems with it. That was not the case with 4.3.1, where a whole lot of problems were reported, and I decided not to install it. I'm still using 4.3.0 (I think, lol).
The next update is rumoured to be a jump to v5.0, which may mean a few significant changes/improvements (or may not). Again, I'll wait a while to see people's reactions to it before installing it.