Oooh - thanks! I have had the exact problem that you describe, and have lost several days worth of mining when I tried to reboot from my office only to have the machine hang. I figured it was just me since my rig is held together with zip ties - nice to hear I'm not the only one having that problem.
Thanks again!
No, it's not just you. Occasionally one of my rigs will have a CGMiner hang, and a look in the logs shows atitweak throwing a hissy fit. A coldreboot often fails to fix it and the same atitweak errors show up in dmesg. For whatever reason a full off/on power cycle cures what ails it.