The Froyo upgrade is essential. Do not listen to anyone in this thread that suggests you do not do it. It fixes many bugs, adds essential functionality and compatibility for current software that you won't get with 2.1.
If some of you have upgraded and are seeing performance issues, you have done something wrong.
Last night I downloaded 2.3.3 from Samsung and installed it on my Galaxy S, previously at 2.2 (and 2.1 before that). The phone has had the issue where no more than 2Gb data can copied since new, along with 2 other phones I've tested. I'm happy to say that 2.3.3 fixes this issue.
I'm not happy to report that the native Email app with ActiveSync is horribly broken - it cannot render html mail, and shows all headers for even plain text email. Reported the issue to Rogers today. So far, everything else seems to be ok.