They seem to use the Class D's I fly out of as practical testing grounds for controllers when they have come out of ATC school. I have to say the vast majority are probably better trained and more professional than 99% of civilian pilots, and to be quite honest they do a much harder job than us too.
Some of them obviously aren't up to it and have to be reassigned to a post where they give out the weather and the biggest order they can give to pilots is 'VFR flight not recommended'. Ripping somebody a new a-hole would be a significant step in that direction, imho.
Bring on Mode S!
(that last bit was being sarcastic)