I have complained about pop-ups and spam on this site before and there is not much difference between them but I heard a very good comparison tonight from Chris Pirillo and I'm going to steal it and use it when ever I can.
What is the difference between an unwanted pop-up or walking into a grocery store and a clerk throwing a can of soup at your head? It's not the best way to advertise your product and chances are you are never going back to that store again. Get a clue, pop-ups suck even more then spam email.