I already had my phone rooted, but I used this process to install the 2.1 ROM today. My impressions:
I have absolutely no experience in this sorta thing, so I found the video walkthrough on YouTube to be extremely helpful. Actually that's an understatement, I don't think I would have figured this out without that video. I had taken brief attempts at installing a 2.1 ROM using other walkthroughs, for some reason beyond explanation this is the only one that makes use of the Droid Root Helper...it almost makes it too easy. Sooo...watch the video and it's not that hard!
Functionality - Overall seems very snappy. I don't know if it was ever an issue with the HC ROM, but the GPS works. Also not experiencing any issues with the live wallpapers, my phone runs just as smoothly with them on. The backlight issue with the physical keyboard is kind of a bummer but I can live with the quick fix (press the sleep button twice) for now.
The only issue that really bothers me, and really has me stumped, is with the Advanced Task Manager app. For some reason, when I end all, my phone kinda lags for a second and then takes me to whatever settings menu I was last in. Could be the phone function, could be the settings to an application, etc. I have tried uninstalling and reinstalling, rebooting, etc etc with no luck. I think I can live with it, although I REALLY REALLY wanted 2.1 lol.
Thanks to the OP for organizing all this info in one place, and thanks to the guy who posted the YouTube video! Loving 2.1!