[Commiseration]

From personal experience, it's not ideal. Assuming they don't lie, and are in reality an awesome person, you can't be with them. You want to, but the distance hinders that. It's no fun being in an online relationship that lasts over a year and it just doesn't go anywhere beyond that...
Also, you can know as much about a person as you can through talking on the computer, phone, etc. but it all changes when you're actually there in person. Sometimes for the better, sometimes for the worse. You find out their annoying habbits, things they don't nessecarily tell you about otherwise, and they just act differently in person. Yes, there are some people who act the same no matter what, but it's definetly different. Sort of like meeting eachother all over again.
Now maybe I've just had bad luck with this sort of thing, but at one point I thought it was an awesome idea too. Get to know them, and someday you're together. Sometimes that "someday" never comes though. Long distance relationships are hard enough the way they are, let alone trying to keep one together with no physical contact whatsoever for years.
Again, it's all my personal experience and opinions here. You can meet amazing people online though and then meet them in "real life." That, I believe, can work under some circumstances. But strictly online for an extended period of time? Been there, done that, not ever doing it again.

-Commiseration-