I've got some new forums, go check 'em out. I'm running bbPress. It's not as sexy looking as Vanilla but it has tagging, better RSS feeds and integrates with WordPress nicely. I like the layout more as well.
The integration with WordPress is the main reason I switched. I want to offer "bonus" stuff on the main site for users who are logged in and this seemed like the best way to do it.
Importing the old forums was a nightmare of course and I'm still cleaning things up. Your old accounts should work. Let me know if you run into any problems.