I had a Mytouch 3g that I had flashed 2.2 on while waiting on FroYo to come out. It's a much slicker OS than 1.6 - which is what I was running. The posts about chewing up battery life are right. I don't know what OS your phone runs now, but I noticed a HUGE difference in battery life. Supposedly 2.2 was going to handle background applications better, but if I ran anything (pandora, slacker, etc.) on my way home and forgot to turn the phone off and back on again it would be dead by morning.
Changing the ROM was really easy. Supposedly there's a risk of bricking your phone - but you can go on youtube and watch videos explaining how to do it if you are nervous.
My phone though, was a total POS, so I got an iphone 3g and did the jailbreak thing, until I figure out what I want to do next. Edge is fast enough for most data I need to send or receive. I get about 150 kbps. Sad, my iphone 3g runs circles around my old mytouch 3g which was supposed to be a newer generation. (No multi-tasking is a minor irritation, I will admit) From my experience, android still has a little catching up to do.. but 2.2 was light years ahead of 1.6.