Definitely worth it, it's literally breathed life back into my 3GS. The phone feels so much faster on iOS 5 than it was on iOS 4. Go for it.
Are you serious ? My 3GS is a joke now. Its so slow just loading up the sms or phone book. App store crashes half of the times I try to open it.
It also consumed all my battery in about 11-13 hours without hardly using it at all (No push or auto sync of exchange etc)
I'm terribly terribly dissapointed and I hope it's possible to change back to 4.3 again.