Dark Messiah (from Ubisoft) will be available on Steam (it is in the Source engine, for those that don't know, and is a weird FPS in an old school RPG setting). Windows Marketplace is relaunched out of the labs just in time for the Vista RC1. Marketplace includes this new Digital Locker system in coordination with major digital distributors. Digital Locker offers the same promise/protection that Xbox Live Marketplace kindly provides: if you pay for it, you should be able to redownload it.
Digital distribution is well on its way to the mainstream, and I'm glad for it.