Jerry, Stephan and Scott have been hard at work updating all of the importers to allow more people to switch over to vBulletin.
The following new importers have been introduced and should be considered beta:
YaBB SE 1.5.4
Invision Board 1.1 / 1.2 Importer

The following importers have been updated:
UBB6 (tested to version 6.3)

The importers are now available in the members area.