Right now I have a FWB. We escort each other to events, see movies together and try to make ourselves available when the other is doing something where having a date/companion is helpful. We often have sex and sometimes we just get together to have sex.
I would love to have a relationship like this one. To be with somebody I cared about enought to have sex with and see for dates, etc.
Even better if she had a high sex drive and wanted to make lots of time for us to have sex.
Ladies - before you start a situtation like this one (i.e., a true FWB) do ask if he is having sex with anyone else? Most of the women I have dated have said either: 1) if we are having sex I want to be your only partner (less an ultimatum and more just rule of the relationship); or 2) nothing.
As far as rule of the relationship, I have felt that their request was simply "I do not want to have sex with you if you are having sex with other women." I thought it was a fair enough request in that I could either agree or move on down the road.