I too had fun with a TS-7200, running NetBSD 5.1 -- nice device! Until recently, it used to drive my home weather station and weather cam (think wunderground.com); it's since been replaced though (see ALIX below). Perhaps I'll save it for a future, more extreme environment project...you know, launching a balloon into the upper atmosphere, or a toaster appliance monitor...I have several TS-7200s as well as a couple of RiscPCs...
Speaking of extreme conditions: please be careful with the GuruPlug version. I gave up on it and ultimately had to return it because of heat dissipation issues. I didn't think ARM devices had that issue, but it did leave a mark when I picked it up the wrong way.I've kept an eye on the Sheevaplugs...
Exploring ARM was fun, but I now use ALIX devices from pcengines.ch: LX800 AMD Geode LX CPU (i.e. i386 port). These are solid devices, are snappy in cpu and io compared to your typical TS-72xx device, and are inexpensive and low power. They don't come with SATA, but they do have PCI expansion. Combined with passive PoE, they are also a breeze to deploy. I purchased an ALIX 3D2 a month ago and easily installed a then recent NetBSD 6. The only thing I miss is support for I2C to get onboard temperature.PC boards such as ones from VIA and the Intel atom use lots more power than the ARMs (up to 15W maybe) and they work embarrassingly well. :-(
Thanks - Joel