I haven't used 2006 for any projects yet because my customers to this point have all been on 2005. There are a few assembly visualization enhancements which I really want to be using. PDMWorks 2006 is a big improvement, and I'm already using that. Photoworks has nice new capabilities with the camera, which I have used for a few renderings.
Bugs are a dime a dozen even in the existing version, so a few new ones may help alleviate boredom more than anything else. If you wait for perfect software, you'll never move forward. The existing version is not perfect.
Overall, though, most of the new features are pretty forgettable. There doesn't seem to be an overall compelling reason to move. This is probably good news, since with fewer changes it will hopefully take fewer service packs to repair.