In contrast to my earlier post, it turns out that we will not be using Vault. For some reason that even SourceGear cannot explain (we are customer #2) we had tremendous difficulty migrating our repository. So for the time being we've decided to clean up our VSS repository and live with it until it causes pain again. I still think Vault is a great product and SourceGear tried valiantly to assist, but to no avail. I expect we will re-assess when 2.0 is released.
Thanks for the update. I have not tried the migration tool, as I used Vault early enough in a project without having to deal with that.
The way how Vault handles labels during migration prevented us to consider move at present. Lets wait if next version with vss style labels will improve.