In some ways NASA has been slow to embrace new web tech, but in other ways it's done really well. For example Spirit and Opportunity, the Mars rovers, were on Facebook and MySpace years ago, posting like they were teenage sisters, sniping at one another a bit. It was great, and really made it fun to follow them. Now, too, there are a lot of NASA Twitter feeds, including one from astronaut Mike Massimino who tweeted live from the Hubble servicing mission (and who has nearly 400,000 followers as I write this).
I just found out via Boston.com that NASA may be planning on inviting people who use Twitter to the launch of the Shuttle Discovery in August. I think this is a pretty good idea, as this could reach millions of people, and if done well could be very exciting and fun. It's a logistical nightmare, of course, making sure all the tweeters have good access including the ability to upload images in real time. I suspect they can figure that stuff out. They're NASA.
Tip o' the spacesuit visor to the outer-spacey Rebecca.