We now know of at least 212 extrasolar planets. All of these (except maybe a few) are what's known as "hot Jupiters" - they're as huge as Jupiter, but they're really close to their sun. The reason for this is always touted as being that our detection methods are biased to find high mass planets (big), and to find ones with short periods (close to the star).
My question now is what percent of stars in the studyable volume of space have so far been found to have these hot Jupiters? If it turns out there's only 400 stars close to us, and 200 of them have hot Jupiters, or 50% of nearby stars have hot Jupiters, then we've definitely more information than a detection bias, it'd would be a real tendancy. But how many is it really?
To answer this question (first order approximation), I'll need two bits of information: (1) how far is the furthest star around which we've detected a planet? and (2) what's the local stellar density? The latter I can find with a little searching, the former perhaps with a lot of searching. If anyone gets the info before me, let me know, otherwise I'll post my results when I have them.