Since photography is all about light, my goal over the next 18 months is to become very competent with lighting (SB-900 purchased, well, gifted (20)!). Luckily, there are great, free resources online like http://strobist.blogspot.com/ aka David Hobby aka Strobist
So on with the learning (new category added).
The main lesson from this was that you control lighting "depth of field" by varying the distance between the flash and the subject and background. The relative differences cause fall-off to be much more noticeable on the background because of the inverse square law of light.
My exposure of the subject was not consistent because I didn't bother being too accurate with flash power and camera aperture settings. The principle is there though and an important lesson well learnt.
For a bit of fun I did put the speedlight to 1/1 power, zoomed to 200mm and did a test shot…I wasn't dumb enough to point it at me, but even at the wall it knocked me out. What power! Excellent tool.