I have never understood how two people could "get to know each other" online. Recently I was traveling with a married couple whom I knew were the lauv marriage kinds from my school - but never knew the specifics of their romance. And they started on topic and I blurt out my logic of how Online Kaadaals is so fatally flawed and suddenly there was this uncomfortable silence and the guy says - "Dei naanum Nayanthara-um (Name changed for anonymity :P) Orkut la meet pannom" - I did not even think of talking anymore for the 2 hour drive.
But, coming to the moot point, if someone who talks to me only over chat/orkut/mail and tries to picture me, I surely know that version will be 100 times nicer than the real me. I chat/blog/orkut only when I feel communicative and I think that's the case with 99 percent of the populace. That is one reason for me to tell me that this is a skewed way to look for a person with whom you would possibly spend a good portion of your remaining life - I say possibly as, though I don't believe in divorces, there is a good chunk of the junta experimenting that too.
But doing some research amongst my makkal who have fallen in lauvv, the popular avenues are:
Rank 1: ORKUT
You should know what "fraanship" requests are. Click here (you have login to Orkut - but I can promise you that you will LYAO - Especially the last pages). Such pathetic scraps touch a chord in equally pathetic female junta and then the comedy starts - minute-by-minute scraps, Crush/Hot List, Messages, Comments on Pics, Fans and then testimonials. And once they decide that they are "made for each other" kinds, you will see some crazy 'holding hands' pics, picture of some rose and all that crappy good stuff.
Rank 2: Gtalk
Gtalk would have gotten the first rank if not for the fact this is like Google, which needs MS Windows to run - Similarly Gtalk either needs Orkut or Blogger (coming up in 3rd rank) - but what with all the status message thingies where you can make the whole world know that you are wishing your special person for their b'day, exam and anything worth saying a good luck for!!
Rank 3: Blogger
The seemingly "intellectual" way of falling in the stuff. I never know why people who write or read a lot (blog, books, Blah!) have this intellectual tag associated with them. Starts off with Anonymous comments, then with name, then both of them blog about the other and then Gtalk and the whole 9 yards plays itself out.
Now you have tools and know-how!! Good Luck!!!