I'm a member of another forum which I'm sure many others here will be aware of (if I were to mention its name) and they actively discourage the use of adblockers. In fact, it was one of the reasons I stopped going there when they started restricting access to members that use such add-ons.
So I guess I'm the sort of visitor they don't want and they'd prefer I wasn't using their bandwidth.
Pistonheads is the only one that I am aware of that does this.
I started using adblock when adverts starting becoming annoying by moving or making noises. I remember the days of MSN when I blocked the flash based advert at the bottom of the program by adding the domains they used into my hosts file.