Heh, I had a similar thing this year. I started getting just gobs and gobs of traffic on a site in a niche so small I pretty much KNOW everyone who ever comes to it. There's a set of ad links on there, and a couple of affiliate ads, but it's mostly just for aficionados of a comedy duo from the 1930's.
Anyway, this traffic was all coming in from Google, and it was all coming in on virtually the same search string. None of the ads or ad links were being clicked though.
Eventually I mentioned it to my mother, and a light went on over her head and she said "Oh - that was a clue on my crossword puzzle this morning!" Turns out I came up first in Google for the search string that a syndicated crossword put out as a clue.
Don't think I made ten cents on all that traffic. But it was a little disarming to see how many people 'cheat' on crossword puzzles by looking the answers up in Google!