I've had several people ask me how I know what search strings people have used to find my blog.

I have a sitemeter.  It tracks the visitors to this site and also how the last 200 (I think it's 200 anyway) people got to my site.  If someone comes directly here it will say "direct referrer," if they come from someone else's blog it will list that URL, and if they got here via a search engine, it will have the URL of the search, which includes the search string in it.  Super easy (and interesting too)!