Troy and I joked about starting an internet porn business instead of recipes, just because it was such a clear money-maker. If only we’d realized there was a great business just a couple of doors down: online personal ads/dating. This article in the NYTimes (free registration required) talks about how mainstream it has become. While makes $240,000,000/year (!) and clearly network effects matter (like ebay you go to the site that has the most people on it, so the bigger you get the bigger you get), in the case of dating they key is finding other people like you so there is plenty of room for niche sites like for Jewish Singles, etc.