Cats love smells more than a lot of things in this world, and I've known several cats who seemed to love sticking their heads right into smelly shoes and boots while they were still warm from the human's feet.
I also know of several cats who seem to have hair fetishes too. Anyone else got a cat who likes to lick or groom human head and body hair? So far I've met two Abbyssians who exhibited this behavior, mostly with their favorite owners but sometimes on other people too.
I've never met a cat that didn't get at least a little excited about feet and shoes. It's all about the smells.
My cats love hair as well. One in particular will "groom" in the middle of the night so you get to wake up with a patch of wet hair.
Dogs seem to sniff out everything, so I have a hard time believing feet are any different. They can't possibly be sniffing for a dog of the opposite sex all day, every day. I'm sure that, like cats (and humans, to a lesser degree), they use their sense of smell to evaluate the world around them and add to their other sensory information.
Also, an altered dog wouldn't really care if there's a "lady dog" around, would he? And if he's not altered, you'd probably know how he felt about your foot/leg pretty quickly. <img src="/images/graemlins/wink.gif" alt="" />
The sense of smell is the most important one in a cat's world. They live by scents. When they are rubbing us, they are putting their scents on us to mark us as their own aas well as showing affection. This is not to say other senses are not important. They are, but smell is above all for them.
Maybe that's what our cats are telling us when they stop by the trash. :-)
A cat's sense of hearing is also many times that of our ability to hear. I try to remember this and be as quiet as I can when I am putting pots and pans away. I don't know how our cats tolerate by boyfriend's tendency to be so loud. He bangs everything he handles. I tried to tell him that the loud noises must be hurting our cats ears, but he still bangs around. Some men are just loud, I guess.