The site must be simple and clean. We will be using a minimum of web 1.0 functionality. Most of the site's content will be featured on a single page and we will use a considerable amount of ajax to move content around.
We want the color scheme to be very bright and eye-catching. Feel free to experiment with color combinations. Remember that we are trying to appeal to a younger audience that will be mostly outside the US.
We will want a logo at the top of the page with a very sparse nav bar below it. Initially, the nav bar will contain just "home", "profile", and "log in" or "log out" (depending on the users authentication state) buttons. We will need a footer for links to administrivia. These are the only static layout requirements.
These components will need to be on the page, but we leave their placement to the designer's discretion. There will be a text crawl, a friend list, and a nav box/bar with links/buttons for setting up friend lists, message lists, and profiles.
We will also need a smaller design to be used in utility pop-ups. This should follow the site's design and should conform to the layout of the main page.
We will want the final psd(s) with slices so we can change text content as needed.
Designers can look at http://www.foursquare.com. We don't want a copy, but it is a good example of the type of simple, clean design we want.