I've been in several relationships with women I met on dating sites. I always talked to anyone I met online as a friend, then took it to the phone and in most cases the conversation never got more sexual than a bit of mild flirting. When it came to meeting them in the flesh though I ended up in bed with all but one of them (an older lady who turned into a good friend for a few years), one of them after about 30 minutes.
They all told tales of guys who only wanted to talk about sex, opened with enquiries about dress sizes. Some of these guys emailed nude photos, none of them got any action. I did and I'm an overweight guy who started online dating at 40.
Basically, most women on dating sites are looking for relationships, the ones that aren't probably only fuck the best looking guys with the most convincing tales of being loaded anyway.