I would say it looks way too much like Facebook, the title bar alone is too much. To me, a site that copies another shows it has no innovation to create something original for iteslf; you even took the exact same colour (#3B5998 ). As soon as (if) you gain any traction in the Social network industry, Facebook will just have you shut down.
I haven't tried out the functionality, but it looks pretty impressive.
Also, as Lemon-tree said, the layout looks way too much like Facebook, and your layout is your first impression: when someone visits your website, they're going to think "Facebook clone", which is never a good thing, because they could just go ahead and use Facebook. Also, I understand that Facebook's success may have something to do with their look, and that's a reason to keep it to themselves, they're not gonna like competiion that looks like them.
Finally, because the layout is the first impression, you are going to have to make it look innovative. The layout can be as cliché as every other one out there, as long as it gives the feeling of being new, and different.
As far as coding... amazing!
As far as design.... as everyone before me said.. way to much like facebook. It immediately took away from the first impression. Use your own colors, use your imagination and make it YOUR own.
As far as who it works.. I didn't try that out. 8)
This may count as spam but i must say that it looks soo much like facebook, tge button color, top bar and the signup section i must say too much like facebook, if you DID make this by scratch *not making statements* i suggest that you change the websites look and feel to it (ex. buttons color and overall look) just so that facebook does not come over and say "we sueing because you stole our look"
Thats all i must say with that and also congrats with the coding ^^
I won't reiterate the common complaint of the previous replies because that horse is beaten, dead, and attracting flies. I really like this site, it's pretty darn neat. I especially enjoy the Answers section (apparently borrowed from Yahoo). One of my dream projects to improve my programming skills is to make a social networking site... too bad my visual sense of design is whack. If you could get in touch with artists/photographers and musicians, some of them may be willing to let you put there creations on your site. And people could upload their own, if it's truly original or you can prove they have permission. Also, look into people who have made such things under GNU or Creative Commons licenses, such as the maker of XKCD.