Slashdot linked up announcement of a new "unified" theory of biological locomotion:

The researchers show that so-called "constructal theory" can explain basic characteristics of locomotion for every creature -- how fast they get from one place to another and how rapidly and forcefully they step, flap or paddle in relation to their mass. Constructal theory is a powerful analytical approach to describing movement, or flows, in nature.

While the article doesn't mention it, to me it also strongly implies that, contrary to other speculation, any E.T.s we managed to stumble across probably will resemble some sort of existing terrestrial critter.

I personally vote for the "hot chick painted green" variety myself. *Oink oink.*