Lots of media organizations are experimenting with Twitter, but CNN is the most aggressive of the big sites.
Commenters at Mashable believe this will 1) give CNN a leg up as an early adopter and 2) it's promotion of Twitter will help push the sometimes difficult to grasp service into the mainstream.
I tend to think CNN is very smart to be near ubiquitous in social media. And that Twitter is role as a multi-platform new channels is growing. Quit looking for the next big thing in mobile, it is the next big thing (and it goes far beyond mobile).
Oh yeah, follow me.