This is very nice... but please change the green color of the bar to any other color, or change the color of the items in the menu... like make it white to appear! About marketing... don't forget to tell your friends and every student at your class about it and encourage them to join.

EDIT: I also advice you to check out this post: http://news.ycombinator.com/item?id=363 so you can know "what people want".. and the features that should be added.

Try to be creative, and look at the link above, so you can get more ideas about enhancing it.