Why use Twitter?

In the future, when I am asked why I use Twitter, I will reference this article by Howard Rheingold.

I'll then add that I have made friends (some of whom I have subsequently met in real life), garnered readers, communicated with fans, established strong contacts in the bookselling and publishing industry, and received a good deal of my daily news through Twitter.

And I've laughed a lot.  Sarah Silverman, Jordan Rueben, Neil Patrick Harris and Justin, the guy who posts the things his...