Assigning tags to user?

Does anyone know a way (either programmatically or through a plugin) to assign tags to users?

I want to build a list of user interests as tags, so I can match related content to their interests.

Cheers,

Chris.

I think this is what you are looking for:
http://codex.wordpress.org/Function_Reference/update_user_meta

Here is a example of how this can be achieved: http://inchoo.net/wordpress/programatically-add-metadata-to-user-accounts-in-wordpress/