I've spent some time with earlier versions of WHS myself, and I've found it to be a great, if frustrating product. While the interface is great, and integration with Windows clients on a local network was fantastic, there were some problems, including the infamous data corruption bug.
Check out our review of the HP MediaSmart Home Server to see what we thought of the original release of WHS.
Thankfully, later releases seem to have stemmed that particular problem, and done something to remedy the instability that my test units showed. So my main bone of contention, the only thing that still leaves me recommending a Linux-based home server, is the lack of apps and add-ins developed for the OS.
Thankfully, the community has responded with some great apps, and Microsoft seems to be making an effort to open the latest version up to more app developers. 'Vail' could be the OS that finally does home media/backup/streaming/file serving not only well, but with a simple and easy to grasp UI.
Remember, this is an early, unstable build, so use at your own risk. And let me know what you think in the comments.
Read more on the release at Ars Technica