I fully agree with you Jon. If one has the motivation and skill for the DIY stuff and can turn out a commercial equivalent, then I say go for it. I'm all about saving some money. Hell, I even made a Sto-Fen-like thing out of an old milk jug that works ok.
Also, I'm not saying that someone will absolutely need every single light modification product out there, but they should have more than just one style for different situations.
look at it this way... you can go golfing with only a putter and a driver, but it ain't gonna be pretty...
The point which shouldn't be overlooked in the DIY vs commercial discussion is that playing around with various DIY ideas teaches one a quite a bit about flash modification variables.
The main reason I went the DIY route originally is because I wanted a diffuser which bounced all the light forward (I use 2 flashes and didn't want a bounce component) and was bigger and a different shape than commercial alternatives like Lumiquest.
I shot some new illustrations for my tutorials over the holidays and as you will see from the photos of the diffusers at http://super.nova.org/DPR/DualFlash/ they actually wind up creating a round reflecting surface which is about 8" in diameter. That's an effective area of about 50 sq. inches and a shape that's ideal for use with a camera flip bracket.
I used a pair of direct flashes for 30+ years before bothering with diffusers and that taught me the position of the light and the amount of fill flash has more real impact on the overally look of the lighting than diffusion alone. That explains why I'm satisfied with the diffusers vs other options such as umbrellas (which I feel diffuse and wrap the light too much to control on a dark background) or the x-small Photoflex SB which is larger and likely more diffuse, but also more cumbersome to transport and set-up.
