Cool! My comments:
On diffusion - I don't really know how it works but I suspect "multiply" in Photoshop would be more like a diffusion map. Also, in programs that support textures with alpha masks (like Infini-D) move your texture to the alpha channel (white shows, black doesn't (depending on the program) so invert it) and make the color channel completely black. Then you can apply the texture with different modes, scaling, etc. and it will act the same way.
On bumps - hey, hook me up with that bump map! I don't remember seeing it in the texture depot. (wait, I found it)
A quick 'n shoddy way to an interesting bump map:
1. New document, 50% grey (in photoshop)
2. Noise (not greyscale, gaussian, relatively high so it all looks like a good even noise)
3. Maximum, to a value that fits your document size. (unfortunately, 10 is the max, but you can apply it multiple times for greater values)
4. Desaturate.
5. Auto-levels.
6. If you want, unsharp mask to a ridiculous amount (200%) and a radius that would take it to about the center of a tile.
There you have a quick, shoddy, but interesting plate texture!
Details - weathering: I hope that you wouldn't make scars and logos that big for a general texture, would you? :eek:
Texturedepot: Geocities isn't allowing you to link it into your frame. :frown: "Open frame in new window" fixes that but it's annoying.
All in all, a useful guide! I would reccommend getting a better diffusion example, though. 
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