I have installed it from USB, but without using the 3rd party software. I use diskpart and bootsect Windows tools only and it runs and works properly. Installed without any trouble.
Yes. I have used "Windows 7 USB DVD Download Tool" for installing Win 7/x64, Win 7/x86 and Win 8/x64 (pendrive Rally 2/OCZ 4GB). No problem (set in BIOS --> booting from HDD-USB).
Ifollowed the steps of the Windows 8 UpgradeAssistant, downloaded it, ( Win_8 pro) and put it on USB flash drive (also saved as ISO), bootedfrom it and installed successfully, very easy.
RMPrepUSB or rufus is better (Even with the time required to work out how to use one or the otther it is still far faster).
Rufus is great. The time required to work out how to use it is about 2 seconds. It even works on XP, so you can "burn" your W8 ISO to USB from XP.