Wow, I was just reading about the SheevaPlug this morning. I was thinking about buying one to play with, and perhaps to make a portable LAMP development server (plus, it'd make a cheap little SVN box as well).
Such device can be great to ship your web products to customers. For example you can create CRM system or web gallery and ship it on SheevaPlug. So client will be able to plug it in his local network and have it working without any complex setup.