I feel that the word "Social networking website" is an oxymoron. If I am on a website, I am not interacting with any human being (please don't tell me that having "friendly" chat with anonymous people over net is networking!). Then how can I have a social networking website. Ah! So you get to meet a lot of old friends, lost crushes, etc. But frankly speaking, save those couple of conversations you will have with him or her about good old days, are you really networking?
So what are basic elements of an interaction?
1. Verbal communication (can be proxied by chats or orkut scraps)
2. Non-verbal communication (an impossibility on virtual world)
Statistically, the opinions we form about a person are not based on "what" she spoke, but "how" she said it. Are you going to base a network just on the fact that you met someone over net?
Ok, so you might say, "well at least you are getting to know a lot of people". Hmm!! but then why sit silent in a bus, train, flight, cafeterias, govt offices etc etc. Start talking... you will get to "know" a lot of people this way too! and what more, the earlier elements of interaction come to your help a LOT faster..
The next argument: "well all of those on net are surely a certain educated mass". Wake up! They are as average (on an average) as any sample of people can be, sometimes worse! (net stalking isnt unheard of).
A very strong argument can be in favor of sites like Linked in. I think till the time I can be assured that its not made to make recruitment easier, I will not take Linked in as a social networking site at all.
Basically social networking is possible only in one way - get out there and talk. It definitely doesn't work the orkut way.