vBulletin 4 CMS and SEO Experiences?

I'm considering a move to vBulletin's CMS. It's still very raw, but I like the idea of having one integrated system. I was curious if anyone made the jump from an existing platform to the CMS. If so, how are your rankings? How is Google responding to the change? What platform did you move from? Any suggestions for others considering the jump.

Interested in having some feedback on the same. Can anybody comment please.

Also how's vB 4 in general SEO wise? Any impact in traffic after the upgrade?

I am particularly interested in hearing from people who have used a different CMS and then migrated to vB4 CMS.