We imported vB4 fine, but since its just a test forum we left out posts and threads, instead we just imported PM's, users, profile messages, forums, etc...
Our DB is huge, a full import would take hours.
I've been grinding through an import on our testbed, but it keeps choking on the user table with a deadlock error. If I hit the browser back button it seems to pick back up where it left off, but I'm worried that it may be missing records. If you have a largish User table (we're at about 160K records) expect it to take a looooooong time to import. We also had to make the tweak to the vbulletin.php that sneakydave posted in order to get the user import to function.
My import on an old forum I use for testing now went well... except the "join date" under my account indicates the date that I installed xenForo... every one else's info looks fine. And the attachments issue, imported from a vb 4.0.7 board.