ZDNet's Ed Bott report on his experiences with Blu-ray and HD DVD under Vista is worth a read. Snippet:
Oh, and about that DRM? CyberLink’s PowerDVD software doesn’t use Microsoft’s Media Foundation Protected Pipeline (Mfpmp.exe). The PowerDVD software is perfectly able to enforce the restrictions encoded on the media by the disc’s producer, without relying on any Vista-specific features. In fact, the software runs on Windows XP with SP2 as well. Presumably, Microsoft will deliver an HD-compatible edition of Windows Media Player someday, which you’ll be free to use or ignore, just as you are today.