In the countless unprofitable hours I've spent looking at what my lovely wife refers to as "motorcycle porn", I have saved a few photos. Actually, whenever I run across a photo of a motorcycle that appeals to me, I save it. You can learn something about yourself by doing that--what I learned by scrolling through that pile of pictures is there are a few common threads in what seems a totally random collection.
I like machinery.
Most of the bikes I like seem to have engines that, well, sort of...stick out. Hang over. Poke through. Lots of old airhead BMWs and Moto Guzzis. Honda CBXs appear. Odd contraptions with Volkswagen engines. Very little in the way of bodywork. Not many regular sportbikes. More Ducati Monsters than 998s.
I'm sure this could all be Freudized into somthing disturbing, but I think it's entirely innocent--I just like stuff that does stuff, and have no affinity for things whose only purpose is to hide the interesting stuff.