WordPress MU

I haven't been around here much for several months and I was wondering if someone could catch me up on what's changed and if there are any new features.

Donncha, if you see this post just give me a quick summary if you have time.

Thanks

Loads of new features but the main ones are:
Uses WP themes.
Lots of site management tools to edit blogs and users, set global options.
User registration form and invite system.
The new version is not compatible with the old version without a lot of massaging of data.

donncha,

in your own opinion do you think that if I were to start using wpmu in a production environment that I would run into trouble upgrading to later versions of wpmu?

Good question.

Upgrading problems: in a word, maybe.
WordPress.com has continually been upgraded and except for minor glitches from time to time hasn't fallen over.
Upgrading software is always prone to failure so there's no way I could say "no, you won't have problems" here.