I post here because I solved the USB BOOT problem (at least in rev 1.4)
first: I tried flashing to the last version F12c (beta) since it was no good, go back to F11, still no boot
Tried plop, as soon as i selected the USB boot drive it freezes, and nothing happens.
Tried to format with HP tool, but no good because as soon as I install linux, it happens again.
Tried like 6 different sizes and brands of flash drives (from 8 to 32 GB) none of them boot.
It is easy to see if they will boot or not, when boot, press F12, then select +HARD DRIVE, if in the next screen, you see your drive, then it will boot.
By accident, I test an old Hiren's boot USB (2GB) and it DID boot!! WOW, we got something here!.
So I start playing and the issue is WHEN the drive is bigger than 4GB.
so, I fdisk MY problematic 8GB Kingston G3, delete partition, then create a partition but of 3980MB (less than 4GB) and set type to FAT32 (d).
then go to the normal install process of ubuntu and it WORKS.
now I can boot ubuntu 12.04 LTS with gigabyte.
Yes, I have half the capacity but that's not important in my case, 4GB is plenty
hope it helps someone, so i doesn't have to lost all day trying to figure it out like i did.