The thing that gets me the most is when you spend an hour typing out a detailed description of a problem. You wait a couple of days for a response then all they do is send you a form letter that doesn't even address any of your questions.
It's like the tech support guy just quickly skimmed through the email, assumed that I was asking something stupid, then picked the closest form letter (usually blaming me) so he could move on to the next one.

This usually happens about 3 times before they finally clue in that I have a legitimate complaint.