Posts: 8,796,049 (visible), total posts according to post counter is 9,527,495 at time of this thread here.
Migrated from Vbulletin 4 and we had to do a multi-step migration from VB4 > XF1.5 > XF2. Total migration time from VB4 forum shutdown to XF2 forum open was around 8 hours, roughly split as 4 hours of export/import + database backups, 1 hour upgrade from XF1.5 to XF2, and the rest was cleanup after importing into XF2 - forums permissions, group permissions, moderators setups etc. Much thanks to the developers of the Big Board Importer without which we would likely still be doing the import if using the built-in importers - we tested the built-in importers when XF2.01 and XF2.04 was released, and by our estimates, it would have taken multiple days (if it could even complete). It was really excruciating to see the post import counter go up by 1 every 20-30 seconds (serious!).
Still working out some kinks but the hard work is done.