I apologize for not having been clear about previous steps taken to correct this problem. What I believe I wrote is that I suspected Chameleon is interfering with my boot process.
I also didn't go over some of my troubleshooting procedures, such as getting into the BIOS menu and telling the system to check its USB first. I didn't mention that because (to me at least) those would be obvious first steps in fixing the problem.
I do not recall changing the BIOS to get OSX to load; however, before posting my initial question here yesterday, I did retrieve and run a BIOS flasher from Acer that reset the BIOS to its defaults (a "just in case" move). This has not changed the behavior, unfortunately. That would tend to rule out BIOS problems, I think.
Essentially, it's as though there is no recognizable OS of any kind on the USB sticks, regardless of which USB port they're plugged into (the machine has 3). This despite the fact that after OSX has booted on the machine, the USB drive is readable, and before the machine boots, I can select the USB stick from the boot disk menu.
That would tend to rule out a fault in the USB bus or the ability of the BIOS to recognize the stick.
I'm using two different brands of USB stick - one is (sigh) a SandDisk Cruzer, but I eliminated the extra software and disk image from it long ago. That USB stick is the one that originally had Ubuntu netbook remix 9.10 on it, which I used to do the original install of Ubuntu over XP. Later I used it to install Snow Leopard. As I've been able to boot from that stick twice before with two different OSes on the same netbook, I don't believe it's a problem with the USB stick's hardware.
The other USB stick I'm using is a generic 2 GB - generic enough that it doesn't show a brand name. Fortunately, it doesn't have any of the "extras" found on a SanDisk model. It, also, will not show up as bootable media. Needless to say, both sticks were formatted with bootable disk images that read perfectly well on a booted functioning operating system.
Again, this suggests to me that it's not a problem with the USB sticks.
Pressing f10 for Chameleon doesn't appear to execute a rescan of bootable media; or, if it does, the USB stick doesn't appear, which amounts to the same thing. The Ubuntu LiveCD image on the USB stick is 11.04, and it does have a /boot/grub directory on it, which - unless my understanding is incorrect - should make the USB stick visible, as a bootable device, to Chameleon.
Every indication I can see points to Chameleon being the problem here. It is the only variable in the entire equation that wasn't present before I installed OSX, and which is now present with my current situation wherein I cannot boot anything except OSX.
Thus, suggestions would be welcome.
I'd also appreciate it if you'd consider moving this thread back out of the black hole, as I believe this genuinely is a Chameleon issue. A primary reason I believe this to be so is that I have, to the best of my knowledge, quite literally exhausted every other possible cause.