With OKCupid, I thought it was implying the selection process is "just OK" -- as in it's a sort of effective but not perfect matching system. Not that the people found are only OK (I personally only ever found crazy people, but I know a few people who got married from OKC...)
I actually don't have an OKCupid account. I deleted it a few weeks ago.
I've heard of other people getting married and a few of my best friends met through a dating website, but yeah. I think that it's not necessarily because of it.