Like Post Tags, WordPress User Tags Plugin allows to add taxonomies under user section, each tag has a dynamic template which displays the list of all users. Template allows you to filter the title and list style.
It can be used to categorize site users to specify their personal interests in various domains. The categories allows to filter them based on the tags.
You can register Taxonomies on the fly, and manage tags for the taxonomies.
Every user can than add tags to his profile as per their interests. In profile section user gets an option to add different tags as per their choices.
Tags section allows auto suggestion as well as creating new tags.
You can also `user_tags` shortocde to allow users to add tags from front end.
For each tag there is a page template listing all the users having same interests. There are filters available to modify listing and content for template page:
WordPress Download Link: User Tags