Recently ran 2 successful imports of VW4 > VW4 on XF using 2 different source & 2 different target databases. However, there are still some quirks in XenForo's debug mode is enabled, and I believe 1 or 2 issues using PHP 5.4, although they may already be fixed in the current build.
So, if possible run the importer with XenForo's debug mode turned off. If possible run under PHP 5.3, if not I think it might stall when importing tagged content. I will be generating a new build in a few hours, once I solve another couple of bugs that have been bothering me today.