Trisk

Sorry to go off topic, but how old are you paulskinback? It might not be hard to find partners in the normal way if you are under 30, or at the most, under 40...but there's a point when it does, in fact, become quite hard to find partners the normal way. How often do you go into bars and/or clubs and see a bunch of 45 year olds or 50 year olds sitting around looking for someone to date? A lot of people, when they get out of a marriage, still feel the need to have someone by their side. It's hard to find that person when you can't go to clubs, when most people your age are married and/or have kids, and when you have a million more commitments (such as kids and serious jobs) than most 20-something year olds have. Not to mention the fact that after 10-30 years of marriage, many people are uncertain about how to get back into the dating "game". So yeah, a lot of them turn to online dating sites rather than lurking around clubs scaring away all the young people in there. You may call this desperate, but I think the internet is actually a great tool for them. I know many older couples that have had enormous success with this.

Aside from that, there are Gay dating sites, dating sites for certain religions...there are people who have trouble finding dates because of some handicap, and yes, even people who just want to up their chances of finding a date while not trying.

There are all sorts of reasons for people to use these sites. Some of them, you're right, may be desperate. But a whole bunch of people have problems finding what they're looking for in person, and the internet seriously ups your chances.
Besides, if you're just looking to get laid and you go onto a sex partner site...I don't neccesarily see where the desperation is. Have you ever wanted to get laid while not in a relationship? One sure way to accomplish this is to go onto a site where a bunch of other horny people want to get laid too. It's much easier than trying to seduce a drunk girl at a club.