http://www.zipp.com/_media/pdfs/technology/rimshape.pdf

http://www.zipp.com/_media/pdfs/tech...spokecount.pdf

http://www.zipp.com/_media/pdfs/tech...spokeshape.pdf

http://www.zipp.com/_media/pdfs/supp...e_flyer_11.pdf

Zipp designs a better rim to address the tire-to-wheel interface "lip" and Bontrager designs a tire to smooth this out, too.

http://bontrager.com/technology/aero_wing_tires

If you want aero rims because they look cool, that's perfectly fine. As Mihlbach said, don't expect them to make you faster unless you are prepared to spend a good bit of money.