Y'see, I've thought a lot about this too because I know quite a few people in online relationships. The verdict I came up with is: It's not a real/true relationship. At most, I can see it as a "pretend" relationship, nothing more than people playing the roles of a girlfriend/boyfriend. As everyone has stated, you need to atleast meet this person for it to become a true relationship. Why? So that you can confirm that the feelings you feel for this person when speaking to them through some medium such as an IM service are the same as if you met them in real life. Once this has been achieved, your relationship bumps up from an online/pretend relationship to a "Long Distance" Relationship, an accepted type of relationship. So if you haven't made plans to meet atleast once in that same year, then you have nothing more than a fake relationship.
So why can't permanent online relationships be real/true?
Simple. You're missing out or throwing away one of two very important sides to a relationship. The physical side. No matter how hard you try with your online cyber sex, no matter how much time and effort you put into writing messages to one another and no matter how well you think it's fulfilling those needs, you cannot satisfy those physical needs in an online relationship. Those of us who are lucky enough to have experienced sex can guarantee you that any experience you have in online cyber is nothing compared to the real thing. The true bonds of love are made through experiences you have together. Walking through a park while holding hands, snuggling on a warm couch while watching a movie, your first kiss, your first time. Without these experiences, you have nothing more than a bond as strong as a wet sheet of one ply toilet paper, capable of breaking at any given moment.
There is also another element that you can't guarantee in online relationships. Trust. How trustworthy can a person be in an online relationship? What's stopping them from having several online relationships? How do you know they are who they say they are? There's no way you can truly know. The thing is, with online relationships, it is possible to maintain several of them at one time. It's just a case of having multiple IM'ing windows open at once. Juggling them becomes far more simple. So when you think you're that person's one and only special person, you may just be one of his many thrills.
There are two prime examples that I have which all of you may/should know about, and I think they justify what I mean well. My apologies for those I mention, but it's for the sake of conversation.
EDIT: Removed the examples as it was unfair on some people. [BudweiserBob!]
So to sum up:
No, you can't be in a true relationship if you keep the relationship online. You just can't. Whatever feelings you are experience evolve nowhere beyond affection and infatuation. Nothing more.