Our team just released a beta of our social bookmarking offering codenamed TagSpace. The best roundup of it is on Dave's blog. This is a really early release - but we're looking for comments in our forum. Docs on using it are available here. Finally, to borrow from Dave's entry:

This is:

• A start, a stake in the ground, a beta demonstrating core tagging and bookmarking features we wish to enhance and develop in the months ahead.
• A social bookmarking service for members of the Microsoft product and technology community. This is the stand-alone service piece, along the lines of del.icio.us or other third-party social bookmarking sites.
• A first-draft tagging service intended to support Microsoft communities first on, then off, Microsoft.com. This is the integrated service piece, along the lines of the tagging features incorporated in sites such as Flickr or Microsoft's own CodePlex.
• A tool for community members to use to begin tagging and tracking resources on Microsoft.com.
• A means for Microsoft.com to begin to aggregate a "folksonomy" of terms that can be used to enrich and enliven Microsoft-related sites and community properties on the Web.

• A replacement or competitor to Windows Live Favorites, which we regard as a different animal intended for a much more general audience.
• A full-blown, feature-complete service with all the kinks worked out.
• A replacement for your favorite social bookmarking service (yet!).