I personally really prefer sites that keep their header/introduction comments really minimal (I think twitter.com does a reasonable job of this). Overall at the moment your site reminds me of a visually modified php forum.
I keep seeing smart people using php to create their web apps, and I still don't understand why. Creating this app in Django or Rails would take days instead of months, and would likely more flexible to boot. I continue to wonder if I am missing something. Perhaps you are using a php framework and I am sufficiently uneducated about php to notice.
Honestly though, its great that you're out there building something, and I hope things go well for you. Simplify, simplify, simplify the visual components and distinguish, distinguish from Twitter (and from a forum), and you will be on the way to making something people want to use.