DAVE!!!!!!!!!!!! Hey dude, what's up? found this place huh? kewl, I learned all the basics from Dave and own 2 of his acoustics.
Using a rasp is how I did the neck on the acoustic I built (thanx to Dave's instruction)
Currently, the work I do is primarily inlay and finishing, but I have changed the shape of necks as well. A rasp works really good on a softer wood like mahogany, but on a harder neck like maple, I've learned the beauty of a band saw with a table you can set at angles, leaving the neck fretboard down allows you to cut various angles on the back of the neck to establish a radius made out of a bunch of small flats, once you have a rough shape (also, it is very easy to maintain symmetry using this method, you do the exact same cut on each side) then you can knock off the corners with a rasp, or good double cut file, I prefer the file as it doesn't leave the same big gouges the rasp does. Then, and I think this is the most important part, when you go after it with sandpaper, first use a block with heavy paper, like 80 or 120 grit. Work your way down to 320 grit on the block. You can then use some 400 to finish up by hand. You don't want to disregard the block, or you end up with funny bumps created by uneven pressure on the sandpaper, of course, there are areas you have to do it all by hand, such as right at the heel, and headstock of the neck, but for the most part, you can use the block.
Routered necks are possible, but you still have a lot of hand finishing to do as a router bit is not a variable radius like the back of a neck, it starts off narrow and thin and gets wider and thicker. The route bit radius is a constant, you still need to finish up by hand, it's basically a good way to remove material quickly. However, router bits that size are very expensive, and custom shaped router bits are worse. Most factory built necks are done on a CNC milling machine of some sort, one with 4 axis capability, this is a wonderful way to do it, if you have an extra $400,000 kicking around, personally, I don't hehehe.