Google recently introduced a new search tool that leverages the open API from Twitter to allow you to find Tweeps that have similar interests. You type in your @ Twitter handle and it returns a search results page that offers up a list of recommended users that have similar areas of interest to you.
A little creepy that Twitter knows so much about me, but it was pretty accurate.
All of the friends that it recommended are related to advertising, and if you were to look back at 99% of my tweets you would probably find that they are all about advertising or some other form of Ad Geekness.
As for this being useful, not really. Up to this point I have been fairly diligent about only following people who are somehow associated with advertising in order to keep my Twitter stream relevant to my interests. So, while I am happy to report that Google's friend finder search tool is accurate ...it accurately produced a list of people that I already follow.