I totally agree that no religion should be allowed to infringe on free expression, whether that be Muslims trying to stop papers from portraying images of Jesus to Christians or Jews protesting movies like "Last Temptation of Christ" or "Passion of the Christ."
But on the other hand, if you intentionally go out of your way to 1. portray their prophet knowing it is against their custom and then 2. make sweeping generalizations about the Muslim religion being extremist bombers then you're sort of an asshole and should expect people to be pissed.
The Jyllands-Posten apologized on Monday, saying it regretted offending Muslims. It said it had not broken Danish law by printing the cartoons, however its editor said Wednesday that he would not have printed them had he foreseen the consequences.
How much forsight does it take to forsee that Muslims would be offended by drawing an image of Mohamad and dipicting his turban as a lit bomb?
Personally as long as no violence is called for against Danes then I don't see a problem with calls for boycotts, but buring Danish flags in demonstrations probably doesn't help the image problem that led to the cartoon in the first place.