First part of the diffusers test: relative quality, light fall-out and shadows.
Canon 20D, EF 28-135 at 28mm, 1/125s, f/3.5, ISO100, tripod, wired remote. All shots taken inside the dining room with high ceiling (about 13 ft), at night (about 10 pm) with no other lights.
Shots taken in "RAW+Large fine jpeg" mode, WB set to flash
Each diffuser measured at 4, 9 and 15 feet, thus simulating head shot, above waist shot and full height/group shot.

Legend for the test matrix:
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BI: built-in flash
PP: built-in flash with ping-pong ball
EX: "bare" 580EX
OB: with Stofen Ombibounce
SF: with LumiQuest mini-Softbox
_1: +1EV in flash
_45: at 45 degrees
_451: +1EV and at 45 degrees