Can I recommend downloading a search query report, find out what folks are querying when your ad shows up, and create a negative keyword from that list? That would help your campaigns I bet.
Yes I would agree, it can be a lot of work..... but the reward can be high. Tools like keywordterminator can do a lot of the heavy lifting for you though. They have a free white paper that explains all about negative keywords and how to find them.
I agree - using negative keywords is worth the effort for large campaigns. No need to pour through keywords line-by-line... You can pull your AdWords search query reports into Excel/OpenOffice and use filters to find out how much you're spending on queries containing various words.