I zoom to 100% by clicking on the zoom bar at the right top and then user the Navigator to move the window around to see the whole image. I use the loupe set to 200% if I really need to see something up close. This is about as easy as it gets and no more difficult than Aperture and in my opinion, much better than LR.
I discovered that clicking on the icons actually zooms (person on the left) out or to 100% (person on the right). View > Show Tools prevents the tools from disappearing which allows quick access to the navigator. That way, I can use the second monitor as a huge 100% loupe. That actually could work for me.
It is
a lot more complicated to Aperture. (1) Double click on image, (2) move mouse to area of interest, (3) press z, (4) check, (5) press z again, (6) press cursor for next image, goto #2 ... You never need to take your eyes from the actual image.
Is there any way to get a better loading indicator? Right now, I click on an image and after a second or so it show up on the second screen at 100% but being able to pan takes another two seconds or so. If you try to pan, you'll end up with an unresponsive spinning beach ball, which I find irritating.
@Manoli:
Thanks for the link to the RAW viewer (which I didn't know about yet) I'm not sure if I really want a separate application for that, though.