Well, I do all the time and this phenomenon is called "Pareidolia". It is the ability of the mind to make patterns from random "noise", such as seeing faces in the fronts of cars by the way the headlights and grill are situated. Also, with something like this :-) smiley face. This happens not only with visual stimuli, but with sounds too - sometimes you may think that you have heard a voice, but in fact it was the result of a mixture of sounds and/or harmonics that your brain translates as something more recognisable. This ability to "see" patterns in otherwise random structures can be seen as an evolutionary advantage - those that spotted the predator in the jungle (the face in the random noise) were more likely to have survived than those that didn't.
My favourite pareidolia effect can be seen on Google Earth (which I'm assuming that you already have and am therefore not advertising for it). Just put in these coordinates, and tell me what you see!
50° 0'38.20"N 110° 6'48.32"W
Post up your own pareidolia photos and favourites - there are plenty around - just look in your burger bun!