On first look, the UI for geofollow is not all that eye pleasing for some reason, but they are spirited in making money. You are allowed to pay to get yourself or city listed prominently on the site. That is the first thing I noticed.
At the top you are prompted to log into Twitter and then add yourself to the directory. They are using OAuth for login I did notice, so a bonus there. I then found a nice video demo of how the site is supposed to work for you.
You can search the directory by City, State, Zip, Country, Tag, Name, Twitter Username, Keyword. So as well as people identify themselves is how easy it is to find them. From there a step-by-step direction is given to get yourself listed and in the best way. Apparently the sooner you are listed the higher you will show in their directory.
After you do a search you are able to select everyone shown and even do a bulk follow, which makes for adding people with similar tags easy.
I did a test search for St Louis, MO and while some results did show for people there, I got a heck of a lot of people just named Louis in their Twitter name. Minor setback. You should be able to specify exactly what part you are searching, or everything.