Twellow is a new twist in almost making Twitter into a yellow pages. You can search for individuals or go narrow into topics to find those will skillsets you need. I read the about pages and it was not fully clear if this was automated or done by some magic hands. But the site is run by WebProNews. I almost see it as a recruitment site, as well as finding those with knowledge on your topics.
The categories are numerous and fairly well defined already. I think there is room to grow in sorting. For example there is no IT type category. So finding someone in social networking could be under media or software or anywhere else. I ran myself and it was not clear what category I could be found in, but they have had me listed since April.
This might prove to be a great tool as I already found 2 new people to follow just by looking at categories.