Pathfinder's solver has been parallel since version 2011.0.0420 (
release notes). The parallel processing feature in that release has been present in every subsequent release and is part of the current release.
It doesn't jump out and get any attention because it's entirely behind the scenes. Basically, there are a few operations (initialization, pre-move, and update) that take a relatively long time for each occupant and we handle them in parallel. It's not perfect (i.e. linear speedup), but it helps a lot. Some of the other performance improvements we made in Pathfinder 2011 are covered in this blog post:
Pathfinder Performance Improvements This post went up before we had the parallel solver.