is your handset jailbroken? if yes then dont update.
if no, get yourself on 3.1.3, its much faster IMO and the apps seem a lot more stable. 3.0 is 4 releases old now, get yourself up to date, its free after all!
3.1 also fixes a number of security issues with the handset
I would say, unless your jailbroken then it is certainly advisable to update