Piracy

Every artist I know uses photoshop - but i dont think even one has paid for it(I would use it too if my laptop was a tad faster).... but adobe is losing loads of money because everyone loves free stuff.(Some disagree)

Personally I think the only practical way to stop software piracy is to have server side software (a la world of warcraft)

that's where web based apps could win.... but FOSS will soon change a lot of reasons.