$11B seems like a low valuation. Groupon is still worth $6B and I don't think its anywhere near half as valuable as twitter. Twitter does have a problem trying to monetize the core business, the only way seems to be to charge celebrities and businesses to send out tweets(advertisements) but that will probably hurt them a lot.
But with all that data and all those users and celebrities there is so much possibility and directions it can go. If I owned them the front page would be all entertainment news, hire bloggers to scan through tweets and write stories about the latest gossip. Why let tmz and other entertainment news get all the ad revenue by writing about the info coming directly out of your site, twitter should be the #1 webpage for celebrity news/gossip. The kind of people who really use twitter are obsessed with this garbage, it seems only natural.