My first reason for the upgrade was to upgrade from using IDE drives on my old server. This box makes it very easy to change SATA hard drives. There's a door at the front which allows easy access to the hard drive bays. You have to mount the hard drive in a runner, but that's just a couple of screws.
My second reason was to reduce power consumption. The old server drew 80W at idle (as measured by my Kill A Watt). The new one only uses 20W, which is a pretty dramatic reduction. At $6 a month, I'm not going to be making a great ROI on this, but at least I'll feel more virtuous about leaving it on all the time.
The box is small and quiet, not a big factor for me as it lives in the basement, but that may appeal to plenty of others. I also enjoyed the humor of the vendor in including a 160GB drive in the package. (I put in something rather larger.)
I installed Ubuntu 10.04 LTS and it worked just fine. For this install I took the opportunity to use puppet - overkill for a home server but useful to give me some devops creds.
Overall something worth recommending but nothing too dramatic - but then I don't like drama in a server.