We looked for them when we were on our honeymoon (DH actually got so hooked he bought the book... Yeesh!). ; We didn't look for them so much this time around, though... still saw a bunch, but didn't go hunting for them (there are Mickeys everywhere anyway... heck, at AK Lodge they're in the bedspreads, the drapes... the carpets.... the flamingo ponds... all over the place!)
I think if you're on your upteenth trip and that 'been there, done that' feeling is starting to creep in, it can be fun to actually hunt for them... or if you've got kids that need a little pick-me-up towards the end of a long day it could probably come in handy as a 'scavenger hunt' kind of thing. ; At the same time, though, if you're going to start kids hunting for hidden mickey's you should be prepared to hear "There's one! ; I found Mickey!!" every 2 minutes *laugh* (Not just from kids, either... I know DH started seeing him everywhere before too long... whether he was actually there or not *laugh*)