Just my FROYO observations... about the battery life.
W/ stock unrooted 2.1 (T-mobile)
(according to the app "System Panel app/ Task Manager")
My Nexus Ones Cpu used to go all the way up to about 998 Mhz (estimate) and drop back down to a 200-300 Mhz area...constantly (every few seconds or so if i recall) with not much running at all..(so idle time was slamming the cpu) this was one of my guesses as to why the battery life sucked.
The other reason.... i suspected... was that whatever is used to calibrate the battery level was flaky. It would go from 100% down to 90% it would seem in about 20 minutes...after that (90% or so) it would seem to stabilize a little. Although when i first got the phone battery life really, really sucked.
I am a moderate user not a heavy user. After doing 3 sets of conditioning it got way better...except for the above mentioned behaviors. With that said after the phone stabilized i got about 12 - 14 hrs consistently.
Now fast fwd to 2.2 "Froyo" (manual install)
Better CPU power optimization...
CPU now fluctuates from about 278 - 333 Mhz "with not much running at all"
if i slowly scrolled up it would be at 278 - 560 or so. (never went higher than that average and certainly no where near max cpu.)
CPU about 278 - 693 with rapid scrolling... again still never shot up to anywhere near max cpu.
After opening and running some apps it will shoot up to max cpu area....
So in theory this optimization should add to the standby time at the very least... in turn getting longer battery life.
I get way better 100% - 90% battery life. (one observation was 2-3 hours...instead of 20-30 minutes)
Also the Android battery icon in the notifications seems accurate now. (may end up ditching the add on widget i got, to monitor battery level)
I have noticed much improved battery life. If you do not get better battery life with 2.2 try at least one battery conditioning set ( fully charge battery until it is 100%...(not when the indicator light is green cuz it will do that at 90%) then run your phone without charging it at all (whether power plug or USB) until the phone shuts itself off. Try that at least 1 time if not 2. I got crappy battery life just after the manual install the first 2 days... until i did this. It maybe coincidental, but it can not hurt to try. It will take a few weeks to get an accurate hours of battery life... but you should all see a an improvement. If not my guess would be some incompatible apps. Example...I did use Helix launcher in 2.1, but it FC constantly so i installed Launcher Pro. Just this morning there was an update that now lets you add shortcuts too the bottom, just like Helix. Launcher pro is very fast too.
One last thing of topic I guess... as far as a new feature in FROYO... i have not seen this mentioned yet but there is now the ability to adjust the text size in Gmail app (like you can in the web browser)...but sadly not in the basic "email" app. So i can now read my emails (in Gmail app that is) without my glasses LOL