What's the benefit of this over email, IM or Skype? I already have communication channels through those mediums for everyone I want to talk to.
Addendum: I just now realized you have a shared viewing feature. But I didn't realize that from looking through your app, but from your description. Shared viewing is what differentiates you from email, IM or Skype. You need to stress it.
That does clarify things, but users still have to go through several steps before they see it. When I look at your front page, the only impression I get is "web based group chat." You should elevate shared viewing to something you mention first.
edit: You do have the material for that, but it's under the "View Sites Together" tab. That information should be what I see first. Looking briefly at your blog, you understand this is your killer feature. You need to make sure your users understand that, too.
Addendum: I just now realized you have a shared viewing feature. But I didn't realize that from looking through your app, but from your description. Shared viewing is what differentiates you from email, IM or Skype. You need to stress it.