I believe you can have friendships with people online, however it is by no means a sufficant replacement for real life relationships. As far as romantic relationships, I don't believe in "internet relationships." It's way too 1-dimensional.
Even though I met my boyfriend on here and we are currently long distance. We didn't label the months we spent talking daily as dating. We didn't consider our relationship to be a dating relationship until we had met in person and spent time together to be able to make a proper decision. There's no way we would go months without seeing eachother. We see eachother fairly regularily, however of course the ideal would be to not have the distance but that is in the process of being remedied.
From my experience, there is just no way you will have the same depth of relationship without being with and knowing a person regularly in real life. Your relationship will lack the depth that is needed to flourish and grow.
I think people should be careful to make sure they don't get so caught up in their online worlds and "relationships" that they lose touch with reality or simply spend too much time online to have the time to nurture and create healthy relationships in real life. The internet is a wonderful tool however it is just that, a tool, that can be used to better one's life and make their reality that much more enlightened, or it can be overused and become much less than a tool, and a mere crutch.