Hey there. Thought I would chime in on this discussion. With the plug computer running 24/7 I would definitely worry about heat. Keep in mind that not only does the hard drive get warm, but the Sheevaplug, with no internal HD gets pretty warm as well. I understand the appeal of keeping it all in a nice little package, but running external hard drives via USB hub gives you the nice advantage of expandability and backup between drives.
Haha and as per the picture posted below of my setup, yes it's quite ugly

, but it was more to give a size scale compared to the Mac Pro below it. In day to day use, it sits on a shelf al neatly tucked away.
Thanks VanHalen for the plug to my tutorial. I sincerely hope it helps you out. Let me know if anything doesn't work or gives you problems. I'm more than happy to help.
Good luck to you both on your plug computer adventures! It's addictive once you get one.....you want to get more. My lust object now for a media server is
http://www.globalscaletechnologies.com/t-d2plugdetails.aspxGrant