I just lost a 5,000,000-step, 11-day WU because I wanted to take one machine off F@H without getting assigned a new WU. I was stopping and starting, trying to get stopped at the right place, and all of a sudden it said "checksum error" and started over with frame 1 of the same job. I just thought it wouldn't be nice to leave a dangling WU with no crunching performed on it.