I am please to announce something I find pretty exciting.  Windows Media High Definition Video (WMV HD) is now able to take advantage of hardware acceleration.  Cards from leading vendors such as ATI and NVidia can now assist in the decoding of WMV-HD files.  Depending on the CPU and video card, you can expect to see a 20-40% reduction in overall CPU utilization.  This is often enough to reduce glitching or even allow for playback not otherwise possible.  The acceleration works on WMV-HD streams that are 720p and 1080p.  This includes all of the content (I am aware of ) on the WMV HD DVDs plus most other WMV HD content you are likely to find around.  To take advantage of it, you'll need supporting hardware, updated drivers, the QFE from the link below plus the required DRM QFE (also on the link below).  If you play any WMV-HD and have a sufficiently beefy display card, I suggest you download the update and give it a spin.

Related links:

Microsoft KB Article with the download link.

ATI's Press Release announcing support.

List of supporting NVidia cards.

The Register announcing the release.

AVSForum thread with details and support.

Update:

ATI's Catalyst 5.6 Drivers claim support for WMV9 Acceleration.