Much of the appeal of Bitcoin (to the people who actually buy and sell things over the internet) involves relative anonymity. They don't want to use credit cards that directly link them to a specific transaction.
The purchase of various substances.
Participating in various activities.
Online dating could reasonably fit that model for many people.
I think that would depend on the type of online dating. For just one time things sure, but if you want to make it something committed then maybe not...