I think the benefits of ChessTempo far outweigh the downsides. But one big beef I have is when the server dishes out a really low rated problem and if I get it right I still get docked rating points!
Case in point: Just now I was served a 1490 and my current rating is 1773. The average time to solve the problem is 27.3 seconds. I solve it in 11. I didn't take any significant amount of time to think ... it just took about 10 seconds of moving my pieces and waiting for the computer to move its. I solved the problem correctly and still got docked .6 of a point.
Granted there are low rated problems I solve and still get positive points, but once in a while I solve the problem under the average time and still get docked.
That is really frustrating especially on a day where I and sucking big time.