A little while back I was checking out the list of the 10,000 most visited websites at pcdataonline and I noticed a free strange URLs popping. They had URLs like www.free-mp3-free.com and www.sex-porn-free.com, etc. (plus a few others I would prefer not to post here). It didn't really make sense to me at first but then it occured to me that perhaps these sites turned up higher in popular searches like "free mp3" and "free porn".
A strategy that I'm considering based on that is to buy up a bunch of hyphenated URLs with keywords that are commonly used to find my site. Then I'll put up doorway pages at those URLs. Domain names are cheap nowadays and I've got my own server so there really isn't any additional cost for me.
But say your site is, as an example, to buy flowers. You buy the domain flowers.com bu also sex-porn-free.com and free-mp3-free.com as well as micro-free-soft.com. So you're going to be getting a lot of bored teenagers, bored teenagers looking for free music, and people who want free Microsoft software or who want to free the world of Microsoft. Not exactly the audience you'd want, I'm guessing.