I've experienced my fair share of nightmares on iOS 4 but seems to have settled a little since 4.0.1 (i'm gonna wait a little before upgrading to 4.1.2 as it breaks the Jailbreak exploit). If you're on 3.1.X there's probably little/no need to upgrade.
Just for the record....my battery life has dramatically increased since upgrading from 3 to 4.
(and yes, the JB for 4.0.1 is super-simple)
It seems at the minute Apple are digging themselves a very
deep grave.....oh well!
Infact.....here's a present
from me to Apple, just incase they don't make any school-boy errors in the next 2 weeks.