Money quote:

My theory: Twitter is in fact the perfect crude technological solution for exhibitionists, for people who are so convinced of their importance in the Big Picture that they believe others want to know exactly what they’re doing at all times.

As described by blogger/musician Jonathan Coulton:
“Just take a look at this Google Maps/Twitter mashup, and then tell me we are not incredibly lucky to be alive at a time when things like this actually exist.”