...never ceases to make me laugh

A recent thread started off by advertising an Empeg for sale - before the end of the first page it has evolved* into a discussion on the personality of cheese mold and cats' uncanny liking for the same.

Another recent thread starts off with a discussion about the PCATS tuner, quickly develops into an analogy of the FAQmaster as a software solution.

What is your favourite rapidly-off-topic thread (preferably with link)?

* Hmm, I'm not sure that would fit with Darwin's idea of evolution...

[Edited: seems only fair that I include links if I am asking others to]