If it's against islam to pictorially represent Mohammed, how do muslims know any of these cartoons are him? I mean surely if they are good muslims, they have no idea what he looks like. Come to think of it, I've no idea what Jesus looked like unless I believe all those paintings of a largely anglo-saxon white man with a beard and long hair! Perhaps I should start burning down embassys!
Of course it is not against Islam to portray Mohammed. I have seen posted HUNDREDS of depictions of the Big M on the internet, as rendered in books illustrating the history of this "glorious" religion. The tipping point was the big M with a bomb turbanned on his head, etc.
As Shakespeare might say "Methinks the Mooslims doth protest too much". Or to put it in more mundane non Shakespearean terms---"the truth hurts".