New PM policy
Invision have issued a patch to add flood control to PMs, which has been applied. Anyone without internal PIE access (that is the various private EVE and WoW forums) is subject to a 10 minute delay between sending PMs.
The PM restrictions and new usergroup implemented a few days ago have been removed.
With regards the spammers, Invision's official word is that humans have been creating accounts and thus circumventing anti-spam measures, before handing said accounts over to scripts who proceed to spam every member. As these spammers will now be reduced to sending PMs once every 10 minutes, Admins will be able to mitigate their mischief much faster.