It's been around at least since the late nineties. That's right, there were new episodes of Xena: Warrior Princess when the TF community was learning how to walk.
One of my favorite old sites that predates Werekatt (though his was the best one by far in those days) was the Transformation Graphics Archive, probably the first TF media/art repository online.
http://web.archive.org/web/200005100....transform.to/