TagWalk is an application which trawls Twitter and collects information about words, users, hashtags and urls. TagWalk keeps track of the relationships between all these things and allows a user to explorer the common links between them.
You can use TagWalk to discover users with a high reputation for particular subjects or hash tags. Or in reverse you can use TagWalk to research users and see what other people talk to them about.
For example, if you consider the hashtag #sql, TagWalk will be able to tell you the users who frequently post it, any commonly used hashtags that appear with it, any recent or popular urls, and which users are addressed in messages containing the hashtag.
The best way to understand this, is to see for yourself, so take a look: TagWalk #sql