I've never gotten it to play .wmv, just assumed it wasn't possible. Would be nice though, as I use Movie Maker to capture my camcorder video and that the only format it'll work with.
Movie Maker sure ain't iMovie, but on my machine it captures better than any other program, and the quality is quite good for the file size. So it would be nice to have jit.qt.movie support .wmv, but if it's a huge pain to program in (or there's some kind of licensing issue), I don't mind converting my files.
On that note, for PC movie work I can't recommend Vegas Platinum highly enough, you get an incredible program for the price---about $80 currently. So those of us not blessed with a Mac or with loads of money can still get our video on.
I can play wmv files fine. This is with Flip4Mac WMV 184.108.40.206 installed. I have just noticed that 220.127.116.11 has been released which apparently "Allows third-party applications to fully import a WMV clip from their application" so am downloading it to see if this might actually somehow break wmv playback.