Well, I managed to get a bit of time this morning to fire off a few test shots.
I used my kit lens (set to 50mm) and available/natural light was from a nearby window, to the left of view, with flash/softbox either on the camera or to the right of view.
On-camera tests:

*Bounced flash was off of ceiling (I was laying on the floor)
Off-camera tests:

*as you can see in the final image, my test subject had had enough and wanted no further part in testing
I plan to have a bit more of a play with the softbox and I will post up a few more test shots in due course.
From this morning's session it seems that the softbox does give a nicer/softer fill-flash effect and it will be good to play around with it further in other scenarios to see how it fares.
aim54x wrote:Will you consider making these out of non-Wheet Bix box materials if someone is willing to purchase?
If I had the time I might, but I don't have plans to do so.
If others are interested I am happy to post up a copy of the plans I drew up (for others to work from to create their own).
Mr Darcy wrote:Hey I wish I had thought to use baking paper. I just used a sheet of A4 photocopy paper. It worked well, at least until it ripped, but it lost a lot of light to the paper. Note to self. Must remake it.
BTW have you had a look at Andrew"s (ATJ) wire frame one? It has the advantage of folding up to fit in a bag for transport/storage.
I originally made a mock-template out of A4 paper to make sure dimensions worked with the lens etc and although it worked I also found it lost alot of light...but the cardboard with aluminium foil on the inside doesn't leak any light and the baking paper seems to do an OK job...perhaps draftsman's tracing paper might let a bit more light through (and be stronger)...but for the experiment the baking paper works fine.
I haven't seen ATJ's wire softbox, though I had read up on a couple of people who had done similar.
If I get to like the trial version I've made and want a more permanent solution then I might go down the "transportable" road....though I think I'd get quite a few looks if I were to go walking around the city with a softbox atop my dSLR
Cheers,
Dave