I've met up with quite a few people I first knew online, typically from various MUDs (anyone play those anymore?). I count a number of them as close friends still, and did end up falling in love with someone I first met over the 'net. We've been together for almost four years now, and living together for three and a half. I knew him for a good four or five years before that as an online friend, however, so we had a good deal of time to make sure that this relationship really was what we wanted. I do wish I'd been single the first time I met him in person instead of living with this other girl that I'd met off the net..she turned out to be a touch on the loony side, something I unfortunately didn't see until we were out of our 'honeymoon' phase, if you will.
So yeah, meeting friends from internet communities is all well and good, but as far as romance goes, I think the ones that end up withstanding the test of time will have a very solid basis in friendship beforehand, much like most other more conventional successful romances.