We purchased a VB5 Connect licence back in April, with a view to choosing between VB4 and VB5 depending on the merits of both.
After a lot of research and discussion, we decided to go with VB4 for the following reasons:
1. We were previously on VB 3.8.7... VB4 was better suited to what our members were used to, and had a lot more options at the time when it came to add-ons and hacks.
2. Our server required a kernel upgrade to allow us to upgrade the backend (PHP/SQL) so we could run VB5. We decided we weren't feeling that
Personal opinion... if you're coming from VB3, you might find VB5 a long way away from what you're used to... best to go with VB4 at this time.