I've wondered about using one... for about 5 seconds. I just buy the pants/shorts with at least 4 front pockets and everything fits in there: phone/ipod, glasses, sunglasses, keys, wallet, ad a camera if I carry it around. I also fit maps and other small papers in there.
I hate using back pockets because stuff gets stolen from there, ALL the time. I'm all up for removing back pockets and putting them at the front!
Also, men should be allowed to wear dresses. When it's 45 degrees outside it doesn't matter what type of pants/underwear combo you have on, it sucks. Also man-fans, same exact reason as above.