Just read this article discussing how popular the Phoenix Mars Lander had become. Turns out that someone at NASA setup a twitter account for Phoenix, as a way for some 'dedicated' space fans to get updates as it made its descent.
The feed was live updates from the lander, and ended up becoming very popular. Something like 40,000 people had signed up toward the end as Phoenix succumbed to the Martian winter.
Nasa was surprised by the response, and is going to use this as a 'blueprint' going forward to engage the public more with the Space Exploration Program.
I wish I had known about this earlier, to me this is an excellent use of Twitter. I've never really enjoyed the 'following' of someone who was just going about their daily life. I think the real attraction of Twitter is when it's something unique or unusual happening, or if the person is unusual as in the case of the Phoenix Lander.
I'm definitely going to be watching for more feeds like this, and I wonder what other unique uses could be found for Twitter. Maybe a server monitor, where a server can scream for help if something goes wrong? It would be much better than a constant stream of status e-mails.