Twitter is finalizing the support for groups, which they call Lists. This is probably the most useful feature people have been requesting for ages. If you currently follow a lot of people, web interface lacks pretty much any organizational functionality. That’s one of the reasons for so many Twitter applications and third-party services. But with this upcoming lists functionality, you’ll be able to group people into friends, colleagues, companies, and whatever else you’d want.
Also, see this blog post in Web Work Daily, which explains how publicly viewable list will be useful as a networking tool.