I know the 1DsIII and the 50D can do this, but it's new to me with the 5DII.

I can frame a shot, zoom in on the LCD to wherever I can focus, focus, and immediately take the shot. I don't even need to zoom out if the subject is unchanging. I have done this both handheld and on a tripod. Yes, I've become one of those people holding the camera out in front of me taking a shot (if I can set a high enough shutter speed).

Even with exposure confirmation adapter I sometime have trouble getting the confirmation beep in low light.

This isn't news to many people. But if you don't have a 5DII, 50D or 1DsIII don't underestimate the focus aides compared to older cameras. Today I've used it both on a Biotar 75 and a Nikon 14-24.

The reason why I traded in my 20D for a 50D was focusing problems with manual focus lenses, especially fast lenses such as Rokkor 58 1.2.

Using live view has made focusing much more spot on. The only problem is that it drains the battery quickly.