For those with 4L lenses, do you find you are still able to get nice bokeh and a nice shallow DOF when needed, even at f4?

This was shot with the 24-105 from about 5 feet away YouTube - ‪Here, fishy fishy‬‏ (http://www.youtube.com/watch?v=ccVfInLFUd8)

f/4 to f/5.6 on the 5D2 is very "Hollywood". It's generally shallow enough to separate the talent from the background, but not so shallow as to be overly sensitive. You can get BOTH eyes in focus. :)

Of course, it depends on the focal lengths and distances.

Also, not all f/4 lenses are equivalent. The 24-105/4L IS is quite nice at f/4 with little vignetting. There are cheap f/4-5.6 lenses that are pretty ugly wide open. That's one advantage for fast primes. They might vignette wide open, but by f/2.8 they're really solid and by f/4 they're table flat. That's generally true of all but the crummiest primes.

Then there's the Zenitar 16mm f/2.8 fisheye. It vignettes to f/11, but hey, fisheye lenses are the extreme!