Well, down with the Austin Flu, I installed MT 5.01 on the blog today. Of course the upgrade didn't go as smoothly as promised and all the stylesheets broke, but that is now par for the course for me. Fixed everything up and it should be running OK now.
The only significant user change that should be visible is that you can now login with your Facebook login as an authentication method, along with several other ID providers. I guess OpenID is never going to take on as planned, but it's nice to see that SixApart is trying to accept as many authentication tokens as they can.
Oh, and rebuilding the site does genuinely seem a tiny little bit faster with MT5. I spoke too fast! For some reason, rebuilding my entire site has ground to a halt. It now takes over 25 minutes for an entire rebuild, whereas previously it didn't seem that slow. Not sure what is going on here.