How often should I clean my coffeepot, and what is the preferred method?
Your specific coffee maker should have instructions.  Mine says every 30-40 pots you brew and it uses the same typical white vinegar method.

I do think it's a little expensive - you basically drain a whole bottle of vinegar.  However, compared to the cost of the machine and, more so, the cost of the coffee it's not a bad deal at all.