I've heard "This will piss the developers off" but in light of the fact they'll probably resell a bunch of their software, this will probably be offset.
It seems they prepared to switch long ago and now it was right time to do it. Transition is also less painful than original 68k->PPC transition. Original MacOS 68k was piece of sh1t, and while MacOS PPC was only faster piece of sh1t - they got it right with OSX. Now switching from PPC to X86 is lot easier.
