So I got a Dockstar, been my weekend project for 2 weekends, and I am well impressed, for the $27 delivered, it has all the CPU power I need. Its a tad short of memory, for example I'm hitting it hard now and its showing 62MB of swap used.
I've loaded it up with being my router and running QoS via iptables and tc and doing torrents, and being a NAS, and the torrents is causing the CPU spikes. So I've ordered a 2nd Dockstar and separate torrents from the rest. That's partly due to memory, I'll then effectively double the memory via two units.
The Sheevaplug I got, I now think it would have been better being a Dockstar, its only doing proxy serving, its 512MB is showing 230MB free.
Guruplug? Forget it. Get 3 Dockstars and spread the load out. You then got some redundancy.
To me, having an external PSU and 3 USB ports is useful, means I don't have to worry about the heat inside the server from the PSU and I can power boot device and storage and USB-Ethernet.
Now about 6 months after I stumbled on Plug Computers, I realize the manufacturers are thinking all wrong. Technically, the idea of Plug Computer is appealing, but they should separate the electrical power from the rest, and then focus on the capability of the server. The Sheevaplug with 512MB memory is probably a good level, but with external PSU. So the Dockstar concept, with more memory. I also think the Sheevaplug concept of USB serial is a good idea. The Dockstar hack of opening the case, or the Guruplug concept of external JTAG, is just adding more complexity.
So for me... now having used 2 Plugs (Sheevaplug, Dockstar), I'd say the right way forward is a unit which is a Plug with DC input, inbuilt console via USB, 512MB memory, SD slots, 3 USB slots, Gigabit Ethernet x2, 100Mbit x1