Using dating sites to look for romantic partners is a little creepy, but I think it's a little more acceptable than meeting someone on myspace/facebook/a forum/irc/imvu/what the fuck and pretending like you have a meaningful relationship. It's a pathetic replacement for actually dealing with social situations. Especially if the relationship "starts" before an IRL meeting.
Of course due to my own experiences, my opinion might be biased.
And that's not to say it's not possible to make friends online. Aside from people I know from forums, I also know people I've met and continued talking to with AIM/MSN/Yahoo. There's nothing wrong with that, but to try and add any depth beyond it is just a cop out.