Quite late at this game. But here goes.
Facebook is quite remarkable, simply. It combines the standard features of a social networking website and the means of keeping the user engaged. The interaction happens at multiple levles, you have the apps that can keep you busy forever and the helpful updates on what your friends are doing (orkut is trying to copy this feature). Possibly the only reason the Indian community will stick to orkut for sometime is because orkut is easier to load on the servers, whereas facebook is noticeably heavier. With speeds being a problem it could take some time to catch up.
From the social websites I use, Facebook is easily the most user friendly, and there is no reason (as mentioned sometime ago in all the debates) it should migrate the audience of linked in et all. If I can stay in touch, network and connect personally then why not?
It would be interesting to see which of the desi sites would get inspired from facebook, maybe something from the TV18 stable ( they are leagues ahead in terms of tech adaptability).
Of course I am in love wiht the blitz app :D