I have a similar 2U tray which I have a PC mounted on, in a 4U SKB roadcase. Underneath the computer is a MOTU 2408 MKII
and a headphone amp. Along with a Yamaha 01v and a 15" LCD monitor, which makes for a very portable rig. Cubase SX is what I use for tracking. The PC is dual boot for Win98SE & XP, I take along Ghost images of both OS's as well. For smaller shows I use the 01v for FOH. For bigger shows I use a stage splitter off the house system. I can record up to 18 tracks simultaneously.
Two years ago I would not of entertained the idea of getting out and about with a PC. I was using a Fostex machine. But the current system has not let me down. Toyed with the idea of going laptop for even more portability, but it wouldn't have as much grunt for my dollar.
I provide the service of recording live shows and rehearsals. Some jobs are weekend blockouts, where I can record a band in their natural habitat. In this situation the PC rig is handy, as the project can start being edited while on site.