If you have special software when you insert your usb key to Mac it allows you to access. Or yiou can actually protect you Mac with password(+usb key). If you are intrested in soft - ProteMac Logon Key is only i know. http://www.protemac.com/logonkey/
The USB flash drive on your MAC does not lock. To remove the USB drive just firmly hold it and gently pull from the socket. Flash drives are a very convenient way to save data from your hard drive.
A recent Mac with an Intel processor can boot from a USB 2.0 Hard drive. Earlier Macs could only boot from a Firewire Hard drive. When you turn on the Mac hold down the Option (alt) key. This will cause the Mac to scan for all available bootable drives. Select the one you want to boot from and it will start up from that drive.
Please see the related link below for an example of running ubuntu Linux from a usb flash drive. Linux is installed on the usb drive allowing you to boot directly from it.
There is no reason you cannot load an operating system on a flash drive. However, getting the computer to recognize the flash drive and boot from it could be an issue.
One would need to buy a USB Flash card reader. they are cheap enough. dont forget to look for a "compatible with MAC" Logo.
Get unetbootin from ubuntu's website. Select the ISO from your hard drive then reboot and boot from USB! Voila!
There are many reasons why your USB flash drive may be not recognised by your Mac, one of the following may apply; - Incorrectly formatted flash drive - Damaged flash module - Corrupted data - USB flash drive detection disabled on your account You should try and use your flash drive on another computer to see if the problem lies with the flash drive, or your Mac. If the flash drive works on another computer, you should check your system permissions, contact your system administrator, or check that the actual flash drive isn't being detected using Disk Utility. If the flash drive does not work on another computer (try both Windows and Mac OS computers), the problem most likely lies in the flash drive itself and should probably be repaired and/or replaced.
You could boot it, but it would never get beyond the initial stages. The setup program looks for the CD after it starts so it can read the rest of the files. Since it does not know how to read a USB Flash drive, it will not find the files it is looking for and will fail.
the creator of the usb flash drive is Dov Moran
Boot it from a usb flash drive
a flash drive or pen drive, or possibly a USB key
A USB flash memory drive is a removable hardware device