Now two different responses needed here. I can't actually remember how I came across AB, im sure I was after some question being answered, Googled it, and ended up finding the answer here- Christ knows what it actually was though!
And the reason why I actually joined? If I remember correctly (and again, i could be wrong), there was a very funny post about lion poo being used to deter cats crapping in ya gardens, and in order to join in, it obviously required me to register.