Dunno. It was quite funny and surprising, but I'm not sure if someone has brass balls here. Or how to measure freedom of speech / joke tolerance is such case.
Maybe - for someone like Colbert - a brave/insane? show like this guarantees stardom and a nice career. Not every comedian gets the chance to make similar appearance... and not every comedian dares to even dream about it.
Then again, isn't insulting an official a crime? Especially if the official happens to be -khm- the highest of them? And in public, media? He could be locked away in totally legal manner and no one could complain about it... It would just be bad for George's already bad ratings. I'm not familiar with laws of US, but I believe there's a paragraph for
cheeky comedians insulting officials

.
Well, there's not much countries where a comedian could pull tricks like this... I can't imagine how such show would end in... Russia, for example. The comedian (to trick the public) would maybe walk off unharmed, but the director(s) of TV station(s) broadcasting such show nationwide would spend unknown amount of time in a small, wet, cold room... and never be a director again. Even if there would be NO repressions, the comedian would be fired immediately, just because directors are afraid of power and trouble it may cause.
If Bush had good advisors or figured out himself (er, maybe not), he would backfire this circus quite easily in his next speech - complain about "everybody not taking things seriously enough", "we're at war, for god's sake" and "enough of comedy", etc. Only way to get rid of buffoon's image is to start acting in serious manner.
Anyway, entertaining. As a comedy has to be. So someone did his work very well here.