I would eventually love to see a Mac client for Windows Home Server so that the Mac status could be monitored and controlled thru the "Computers and Backup" tab. Perhaps somehow tying into TimeMachine if the SDK for TimeMachine is open enough to do that.
Also, I would like to see the Media Shaing support the entire range of codecs that the Xbox 360 supports. Being a Mac guy, all of my music and videos are in MPEG4 or H.264. While I've installed TVersity on the WHS machine to get around this issue, native support in WHS would be much nicer and cleaner.
The automatic backup features on my Vista laptop is incredible and I love the ability to grab my shared files from anywhere with an internet connection. So far I haven't run across any bugs in the RC version. Congratulations WHS team! You've really made a must buy product here. Can't wait to buy the final release.