I like the concept. It does resemble twitter in some aspects, but you can differentiate it somehow to increase your chances of success. Some other notes about the design:

- Simplify. It looks busy. - Get assistance from a web designer to help with the layout and colors. - Don't put ads on the home page. - Even on the other pages, use less ads. Especially lose the flashy banners. Why does the registration page have a big flashy banner at the top?

Good luck.