I'm playing with a 1.6GHz Fit PC with an 8GB SSD at the moment using Ubuntu Server and OpenBox window manager. It will boot from cold to the app running (it's a touchscreen frontend client for my broadcast control system) in just under 30 seconds. That's with 12 secs of BIOS and no tweaking on the OS side. Although I can't seem to get Bootchart to run on it, so tweaking will be a bit more involved than it otherwise would've been.

The one I have only has 1GB of memory, they sell a 'GTI' version with 2GB and a 2GHz CPU. Stick a 1TB 2.5 inch SATA disk in it and you're good to go.