I know a lot of guys that use OKCupid and it works great for them. But they all live in either the US, UK, or Canada, so there are tons of girls that use it there too. Of course, it must work for other countries too, but naturally, it works better where there are more users. People I know use it primarily for booty calls, and it does that job fairly well. However, these are all guys that have no problems picking up girls in real life, are good looking, and socially pretty well versed. They only use it because they don't want to jump through the usual hoops, and this is much quicker (barring the possibility of driving a certain distance to meet up with the girl).