An excellent, though short, piece on Mashable today about the pros and cons of putting Twitter up for sale.
I am impressed at the lengths Facebook has gone to in their bid to clone/outmaneuver Twitter's features and appeal. FB has made it clear they see a rival in Twitter, and they're interested in being the top dog in Social Networking conversations once again.
I like the suggestion that Twitter sell to a company such as Google or Apple. If they did end up selling to Facebook there's a very good chance their unique service would be buried under the multitude of communication features on Facebook. I enjoy having different conversations on the two networks and worry that Twitter would disappear in such a move. If they were bought by a company that is known for making various, unique web platforms and fostering real development (as is Google) they would gain both the support to become a top social networking service and the security to keep them from being absorbed along the way. It would be nice to see them continue on their own, but the climate is beginning to feel like Facebook is in for the kill and Twitter needs some protection.