As a bit of relief from the economic gloom and doom I wonder what is the longest search string you have ever had triggering one of your ads? To get the ball rolling and set what I think might be a pretty "hot" target here is my entry (I kid you not); "Where can I find a black and silver ring like the one Michelle was wearing in Coronation Street last night?" One has to admire the searcher's faith in Google but I think it will be a while before semantic or personalized search reaches such levels of comprehension! (For the unfamiliar, Michelle is a character in the long running UK TV soap opera, Coronation Street.)
I have had "how do I clean a silver antique vase without damaging the metal and does not require gloves to use"