Well I have to hand it to Twitter, this is a really interesting move. It's far too early to call whether its going to be a stroke of genius or not but it's a really smart thing to test. 

Twitter have been languishing quite a bit lately but they do have a huge network and delivering content to that network makes a great deal of sense. Also, I don't think it dilutes or cannibalises their offering in any obvious ways.

Hat's off and good luck to them.