Differences to the outgoing G11 are rather thin on the ground. Externally, the Canon G12 body is about the same as it's ever been, although you won't find us complaining. It's still well-adorned with dials and switches, and while that's intimidating to beginners, for those comfortable using a manual mode it's an absolute godsend.
For instance, on lesser compacts - and even many low-end DSLRs - changing the ISO requires that you give the menu system half a dozen prods. The Canon G12 has a manual ISO dial right on the top, with the mode dial sitting on top of that in a kind of wedding-cake arrangement.
On the left-hand shoulder there's a dial for adjusting exposure compensation, while the back of the G12 features a secure, solid-feeling jogwheel for scrolling through the menu system.
One addition to the Canon G12 is a dial on the front of the camera, which is designed to be used by your shutter finger to dial in shutter speeds or aperture settings. It's arguably quicker to find and use than the solitary wheel on the back of the G11, as it requires you to move your shooting hand less, and is very useful in manual mode, with the front dial operating shutter speed and the rear wheel changing the aperture.
Like the G11, the Canon G12 has a 3in, 461,000-pixel screen, and it remains one of the best examples you could wish to see. It's bright and extremely sharp, which is makes it superb for checking focus and making adjustments to your settings.
It's so good, in fact, that the presence of a tiny, cramped optical viewfinder above the monitor is a mystery. It's too small to be even moderately helpful: use the LCD instead.