None at this time. 4.0.5 has some serious issues. It's complicated for those who have not been in the back door. It's server resource intensive. You think you're having server issues now, just wait.
The CMS does 200+ queries just sitting idle.
Mods for VB3.x do not work on VB4.x. And a lot have not been updated.
The user profile customizing is not in the current version and is not slated to return until VB4.1.0.
The stylevar and css setup is more complicated than it really has to be. A lot of customers using VB are not programmers.
VB uses an in house varible system that has little to no explanation about it.
It's outragously expensive. In US dollars the suite is damn near 300.00.
VB does not play well on a lot of shared hosting. Unless you find a good host that is up on VB's needs.
Finicky about what versions of PHP and MySql it will operate with.
And on and on and on...
If ya'll want to upgrade that bad I reccomend doing what I'm doing. Waiting for VB 4.1.0. It promises to:
Clean up the styling system
Fix most of the bugs
More real world usable features
Patients ya'll.