I am sure it happens, but I would be willing to bet that more often than not, it doesn't work out. When your only communications are online, your relationship is a mix of reality and fantasy. You only know the side of the other person that they are willing to show you. When you meet in real life you might be pleasantly surprised, or your fantasy might come crashing down.

There was a couple that were quite active here a couple of years ago. His_pita and her_Joe (sorry if I got the names a little off, just going by memory). She left her husband and moved in with Joe without a previous in-person meeting. It seemed to work out very well at the time, but I don't know what has become of them over the last couple of years. I would be willing to bet, however, that they are the exception rather than the rule.

Good luck!