Some progress. I've been working on the 7.2.1 update, but working on the importer as well. I have the users/groups/categories/forums portion done. Now it's a matter of topics/posts/polls.
A couple things I've run into so far. vb does a double encryption with a salt on all of the user passwords. For that reason, the passwords can't be imported (they are, but they don't work). So, everyone will need to request a temporary password after the import has finished.
So far I haven't been able to import the group/forum permissions. I'm not sure if I'll be able to resolve this one. If not, then forum permissions will need to be set once the import is done as well.
Once 7.2.1 is out in final then I'll work on getting this finished up.