http://www.techcrunch.com/wp-content/uploads/2009/03/newprof...
Twitter made an identical change in September of last year, described in their blog post here:
http://blog.twitter.com/2008/09/changes-afoot.html
The interesting thing is that the rationale is exactly the same for both companies, yet Facebook users already have the ability to form adhoc groups and filters of their contacts, whereas Twitter doesn't. It's probably a big part of the reason why my Facebook friend list feels pretty manageable at close to 300 people, yet following a similar number of people on Twitter drives me a bit nuts and my Twitter feed increasingly feels like a crazy RSS reader with only big giant folder and no sorting abilities. I've been trying to deal with the info firehouse overload by going old school with browser bookmarks and grouping twitter pages by "friends", "designers", "San Francisco", etc.