I just tested mine in the field this past weekend. Mine worked reliably well for most of the evening (wedding). However I was never more than about 25 feet away from it. I got the Flex's mainly because I love ETTL flash and I needed my flashes to go off in bright sunlight which I couldn't with the ST-E2.
I find that 580EXIIs work well, 430EX II's are the best as pocket wizard states. My buddy's 580 EXI's were doing OK, but much more inconsistent (in exposure) than my EXII's.
At one point, I had a mini on top of my 1D, an 580EXII on top of the mini. 1 430EXII on a stand to the left and one 580EXII to the right and everything poped for some very nice fill. That made me smile.


