I put a rooted vanilla version of Android 2.2 "Froyo" on my Motorola droid a few days ago. Here are my observations.

It's faster.
Not a mindblowing speed increase, think the feeling you get when you compare XP to 7. 7 is faster, but you can't specifically narrow down where.

I haven't gotten flash.
That could be a result of me updating my phone on my own with the rooted version, but regardless, it's still not in the Market for me.

I like the new dock.
There are static icons for phone and browser down at the bottom of the page. They are either side of the app drawer, and there is a total of 5 home screens now. I like having two of the most frequently used items be on every screen.

There is a new screen lock
I can now use a pin based key, it always bothered me that I couldn't, and I am now happily using one.

The camera app is more polished.
The controls are now much easier to get to, and it could just be my bubbling happiness affecting my judgment, but pictures seem to be taken faster and be of slightly better quality.

Geo-tagging pictures.
For some reason, it had been turned off. I had explicitly turned it on at one point, so that was a little strange, but thanks to the easier camera controls, it was very quick to restore.