Out of three girlfriends (one being current), I met two of them on OkCupid.
I highly recommend the site, especially if your standards aren't absurdly high like mine!
Overall though, the site works very well, and there certainly has a mix of people. Depending on where you are, you'll meet normal people based on your area, it's pretty "non-desperate", but be prepared for a lot of guys sending "Hey, sup?" messages, and looking for sex if you're a girl. It's basically like normal life! :bleh
I'd only date a girl (and do) who is up to my standards (blonde, tall, thin, etc.) so it took awhile to find one, but there were plenty of reasonably attractive and average looking girls, sure it'll be difficult to find that "perfect" girl, but there out there, I found one! If you want advice on writing messages to people, don't send a short one, but don't make it really long, be yourself, don't exaggerate, and answer the match questions. Try and relate yourself to her in some way when sending a message, say mention one of the bands she listed as liking, or a movie, try and use some humor in both your profile and message, but don't overdo it. For example I said "Besides for being a raging egomaniac I consider myself a pretty amazing person!" just work some humor in, but don't go overboard. Definitely don't compliment her on her looks in the first day or so of messaging, pretty girls get compliments all the time, be the guy who says "You watch Tarkovsky films too?" not the millionth guy who said "Man you're really pretty".
Send me a message if you want some help writing your profile.
Ohh side note, never say "Hey" in a message, pick something that stands out like "Heya!"
Talk about yourself on your profile, don't brag, be honest, but sound interesting, do you have any (non-lame) talents, or interests? I didn't mention that I have $500 of Dungeons and Dragons books on my profile, I mentioned that I have my Black Belt in Taekwondo, that I'm in the Marine Corps, etc. If you see a girl who mentions she likes a similar nerdy activity, then mention it. Don't get discouraged, I sent 10 messages for every one reply I got, but you should only need one girl