I'm on T-Mobile and have had about a month with my phone. I've tried out different things on it (like tethering) with success. After reading up on this site about the 5.0 OS I decided to bite the bullet and do the upgrade without waiting for T-Mobile.
Thanks to the in-depth walkthrough on this site (complete with pictures for folks like me) I was able to get 5.0 up and running on my 8520.
In addition to the upgrades that have been documented already I got an added bonus. I now have full bars of service in my house when I never did before. Browsing the web and sending MMS are all noticeably faster as well.