I called Verizon to complain about 2.2 update that has made my D1 slower . The guy told me I should'nt have more than 12 downloaded apps and that would make my phone run smoother and faster ? Is dude high or is this the sad truth of of Froyo -2.2....
That's a bunch of hoo-hoo...I have dozens of apps on mine and no issues.
Best thing to do is a factory reset (Settings>Personal) - that can clean up lots of hard to diagnose issues. 2.2.20 is quite fast on my D2, you may have a few bytes crossed.
Make sure you aren't running any task killers/task managers, android doesn't need 'em.
If you have a bunch of widgets on many home screens that can slow things down...reduce your widget count to what you actually use. I recommend Launcher Pro rather than the stock launcher - faster/smoother and much better feature set.