FWIW my experience is that it depends on what effort you put in - I've tried a number of sites with various degrees of 'success' which depends of course on what you want!
There are definately fake profiles on all of the sites I've tried but a bigger problem in my opinion is that the 'systems' send you loads of fake messages when you join for free in order that you'll then pay to join to answer these messages which then obviously leads nowhere...
However to suggest as in the old posts on this thread that fake profiles are maybe 75% is _in my experience_ nonsense esp as on most sites women join for free but men have to pay for anything over a basic package which usually means little or no contact options - unfair, yep, but that's the way it is and the men on these sites still way outnumber the women who can then pick and choose...
I'm in the UK and have used Adult Friend Finder (AFF) off and on for years - mainly as a non paying standard member and trying to chat to women using the instant messaging (IM) system - and in the past the free chatrooms although that's usually pretty futile as the distances make it going any further unlikely. Ok if all you want is cyber sex with someone in the US - tried it but not for me although she didn't have a webcam!
Have chatted online on the IM system to dozens of more local women over the years - sometimes a one-off conversation, other times on a regular basis - most of the time it doesn't lead anywhere - and is frustrating because they're usually chatting to a number of men at the same time so the conversation is painfully slow. If you can get them to chat off AFF - chatting on yahoo, live etc and then exchanging pics, mails, texts etc again_in my experience_ most of the time it doesn't lead to a meet - but I'm also fairly cautious as there some very odd people out there...
My first free 'stint' on AFF eventually led to a couple of 'social' meets and 1 no show - I met one woman a number of times but no sex and the other was one-off social meet that I think we both decided wasn't going any further!
At one point I paid for a couple of months on AFF but didn't have any success - lots of chat but no action - so cancelled.
Since then over a period of years as a standard member, I've met 3 women off AFF - 2 earlier this year - and all resulted in sex and all ended up being a one-off as I guess it wasn't right for either or both - I'm really looking for a regular fwb. A couple were fairly quick - chatted off and on for a few weeks or so, the other we had chatted for years and eventually it led to more!
Also had success on Illicit Encounters a few years back within a day of joining - paid - and met the same woman twice in a few days for hotel sex but that was the only success and even back then it was very expensive so cancelled after a month!!
Also had some success with Sex in the UK - met a couple of women, one ended up having sex on second meet and the other we had agreed just to be friends.
Because there's way more men on these sites it seems to me that you have to be persistent in that it's a numbers game so the more woman you try to contact the more you're likely to eventually find the right person for a meet but it can be - and usually is

- very frustrating.
I'm currently a non paying member on a few sites including AFF and as it looks like I'll have a bit more time over the next few months I'll probably join one or two for a month to see if the contact options lead anywhere.
Overall I don't think these sites are much different than more conventional sites - possibly a little more honest over why you're there really - and again FWIW I would suggest doing a bit of research on the number of 'matches' in your area, check em out for free and then if you think it might work for you give it a try for a month or two which usually costs less than actually taking someone out...
Happy hunting...