In the category of sex & evolution I would be remiss to not post on this, even though I am a bit late to the game...
Just in case anyone missed it, I should at least point out a recent paper, "Coevolution of Male and Female Genital Morphology in Waterfowl" by PLR Brennan et al. in PLoS ONE. The study was the subject of an interesting article by Carl Zimmer in this week's New York Times, which has met with considerable discussion in the blogosphere including this nice summary by Coturnix.
Not only is the long and twisted penis an interesting feature itself, the correlated complex morphology in the female genital tract makes this a really provocative case of probable sexual conflict driving the evolution of genitalia.
The image (of an Argentine lake duck) comes from a 2001 paper published in Nature, "Sexual selection: Are ducks impressed by drakes' display?", by KG McCracken et al.
How dumb is too dumb? We still don't know!
2 hours ago in The Phytophactor