Interesting - I thought by having a 70-200 II I'd do away with the 135L or is that extra stop worth it? I was debating buying the 135L when I already had the 70-200 f/4 IS but figured 2 stops was a big enough advantage.
I own both the 70-200 2.8 II and 135L and use both frequently. The extra stop of aperature on the 135 comes in handy at times. The 135 is also lighter and less conspicuous with a shorter minimum focal distance (which helps in tight quarters). I use the 135 much more for indoor portraits and kid shots. I use the 70-200 outdoors more and for indoor sports. You probably shoot different things than I do, but both the 135 and 70-200 2.8 have a permanent home in my kit.