http://www.washingtonpost.com/wp-dyn/content/article/2008/11/12/AR2008111201565.html Twitter has exploded in popularity since it launched in 2006, and shows no sign of slowing. This is real economic growth you won't hear about fomr the doom and gloom media. Thsi is more proof the US economy is still fundamentally strong.
Ads. Although twitter isn't profitable thats not important as long as the userbase continues to surge. As the number of users rises the cost per user falls.
When I first heard of twitter I thought this is the stupidest thing. When I first saw it I thought it was even dumber. However, a couple friends had been using it for marketing purposes and kept saying how great it was, so I followed them. It's amazing as a selling tool. I think totally worthless otherwise, but if you have something to sell, twitter is amazing.
Not really. You can theoretically start a company and then 'pay it' $1,000 and it would technically be profitable, but a really crappy company.