The sex trade is an example of a trade where bitcoin offers few advantages over cash as you have to meet face to face anyway.
Actually thinking about it maybe there is an advantage of plausible deniability. You can claim no cash has exchanged hands, they would have to prove you sent her the btc, and that is assuming prostitution still counts as prostitution if you pay her in btc?
We could make this work
BootyCoin? For all your deep web booty calls.
heh