I'm ambivalent about these sites as well.
I signed in one of those sites for a month (parentsalready.com), I was not looking for a relationship but just for people in the area that were in the same boat as I was (single, with some free evenings and nobody to go to the cinema, theatre, dinner with asmost friends I have are married therefore don't have the flexibility I now have.
My impression of these sites is a bit ambivalent:
On one hand everybody is trying to sell themselves so hard that they don't portray their real selves (albeit they do what they aspire to be). Photographs are just resemblances of the real person (I say that because photographs never "reveal" my real self, I always look awful or prettier than what I am, although perhaps I'm severely deluded and I actually look as awful as in my photographs).
On the other... All people in that site had children which was great as I got to chat with many people that were going through the same I was or who have been there. There were obviously some messages that were not worth opening forget about replying to them but, I met a very nice guy who had very simmilar interests to mine, and was not in a hurry to find someone either. So we became very good friends and he has provided a lot of support in difficult times, and has been an incredible friend. Yes butterflies in the stomach and all that but as much as I liked him and he did, there were some circumstances in our life that would have caused problems in the future so, I have left it at friends stage.
The paradox of this is that this new friendship "pushed" me into re taking some interests I have put in hold, and while at that... I found my Mr Right