It looks like they converted from a public company to a private company again -- a reverse IPO. Probably vBulletin was a very small part of the decision. Looking at the overall deal, I cannot imagine how such a high valuation was justified.
I had the opportunity to work with IPBoard recently and it's made good progress. It's a real competitor to vBulletin. Wordpress, Joomla, and Drupal also have forum plugins which will put additional competitive pressure on vBulletin. vBulletin will either get better faster or it will see it's market dominance erode rapidly over the next few years. Probably it will be the latter.
I can't upgrade to vB 4.x because of plugins we use which do not support 4.x -- and may never support 4.x. This could be a serious problem for us.