I took a quick look at your site and it looks very nice! I didn't look for the "continuous YouTube playback", but that sounds quite impressive. I don't know what your goal is with your site, but if it is more than just a playground, then I would be a little concerned about how you are probing/polling your server in intervals on the "wall". I imagine that your server could quickly get busy with a decent amount of users. You may also want to reconsider the data that you are transferring within your JSON. It looks like you are sending along a list of friend IDs; having many friends whose IDs have to be transferred every 500ms (?) for several users could do bad.
In the end, it probably doesn't matter (at least not for quite a while), but I just had to comment on it.
Other than these details, I like what you have done!