I'm not sure of the exact number, but tonight I saw GPUGrid wasn't sending me work on a Linux box because it didn't have enough disk space. There's plenty of free space on that machine so I just upped the allowances in BOINC and work started flowing again. That system has been online with the same settings for over a year, so I'm not sure why that happened. Anyway, if you're not getting GPUGrid work check your log for a message about the acemd app needing more disk space.