I gotta believe that some of the problems people are having are related to loading a 2.2 ROM over a 2.1 ROM without any data wipe of any kind. I'll spell out what I mean for those who aren't rooted and don't have experience with loading custom ROMs.
When 2.2 was leaked, it was a well known fact that a Data wipe (factory restore) was HIGHLY RECOMMENDED to run 2.2 without issues if coming from 2.1. I personally wipe much more than just my Data partition (factory reset) when switching ROMs (even between 2.2 ROMs). All of the problems I am reading about I see everyday and my first question is "Did you wipe data prior to flashing this ROM?"
What's my point? If you are having serious performance problems after 1-2 days, go ahead and do a factory restore. You will still have 2.2 but you WILL LOSE ALL OF YOUR SETTINGS, CALL LOGS, ETC. Google will back up your apps from the market (both paid and free apps), contacts, Gmail calendar objects, etc.) but without an app like Titanium Backup (which requires Root Access), you will lose quite a bit.
Beats having a really slow phone though!