That's not true! You can put screwposts in a vacuformed case; the black duct tape is to cover up the fact that it fits together poorly. I don't mind vacuformed cases; they look really great, but too flimsy for my tastes. Also, I'm too cheap to build a vacuform table. Like I said, really love the look, but would not use one myself. You could build a case but I would never be able to build one that looks good.
Right now on the YAP64 I'm modifying the existing Wii screen frame-case thingy. I would not do it again. It is not built in two halves; it fits together in a really stange way. It also requires sides to be put in, and mine don't seem to fit because I suck at building. Next time I would use a premade case/frankencase. Premade cases are easy to work with, usually durable, and can look very professional (but not creative). Frankencasing is cool but I don't really have that much to work with. Need a cool sort of case.
Next project after (or simultanous with) YAP64/2 will be a GOAC-with-SD in a computer game case (like a DVD case but 2-3 times thicker).