Portable Mac apps on a PC formated USB flash drive How-to...
For those who use both Mac and PC. There is a way to run both PC and Mac portable apps on a USB flash drive seemlessly by creating a HFS+ formatted sparse disk image directly on the FAT formated USB flash drive.
First there is a website for portable apps for Mac at http://www.freesmug.org/portableapps where you should download Portable Firefox, Portable Adium, Portable Thunderbird, etc.
And of course http://www.portableapps.com for PC users.
Second, format your USB flash drive as FAT (MS-DOS) if it isn't already.
Third, on a Mac, go to "Disk Utility" and select your USB flash drive, then go to File-> New-> Blank Disk Image. Type a name for it, select a place for it (your USB flash drive), select a size, but make it around the size of your USB flash drive so you have room on the disk image for your portable Mac apps.