I do have some ideas around guiding the user through the initial experience outside of the initial overlay and get the immediately involved with interacting with others. I think opening up the lines of communication between the users immediately is key.
With regards to the Facebook login I understand your point, hell I've said it myself about other sites, but in this case the entire experience is based on the data from your Facebook profile. It encourages honesty about who you really are and makes it so it is not another profile for you to manage. Without the ability to use the Facebook data you wouldn't be able to have much of an experience. I understand that a percentage will walk away from the site due to that but I'm going to have to focus on the millions of people who do use their Facebook account on a regular basis to login to a third party site.