I needed a new lens for indoor sports, as my 70-200 f/2.8 IS forced me to use ISO 3200, which produces too much noise. The 135mm f/2.0L is perfect for that use on my 20D. Fast, silent and precise focusing, low weight (the 70-200 2.8 IS is a brick in comparison), it handles very well and the build quality makes it a joy to use. It is VERY sharp. I smile every time I mount it on my camera cause I know the photos will be good.
If you look through the lens from the front, it looks like a WIDE tube filled with glas.
The lens is perfect for portraits - I don't find it too narrow on my 20D. The DOF is very narrow at close distance, so unless you're directly in front of the face or stop down, you can't get both eyes in focus. Obviously, this effect makes subjects in focus really stand out.
The lens should be well suited for concert photographers located in the pit: its wide aperture is the only thing that helps for fast-moving artists on stage.
There is a little bit of play in the focus ring along the optical axis - from other reviews I hear that this is normal.
The 135mm f2.0L is my new favourite lens.