What is Twitter?

(1) "It's one of the fastest-growing phenomena on the Internet."
(2) "Twitter is the telegraph system of Web 2.0."
(3) "Twitter is the first thing on the web that I've been excited about in ages."
(4) "Incredibly useful"
(5) "I really like Twitter."
(6) "If you aren't familiar with Twitter, it is one of those things, like MySpace, that sounds totally ridiculous and stupid when you first hear about it. But once you start using it, you realize how much fun it is."
(7) "When I first started doing it, I thought, 'geez, not another website to worry about updating and checking', but now I'm glad I did it."