The Mac by default formats Geek Sticks, SD cards and their ilk as FAT. If it's under 4Gig as I recall it defaults to FAT 16, over 4Gig it uses FAT 32. (FAT 16 won't handle anything over 4Gig in size.) For what it's worth I've actually found that the Mac does a much better job of formatting these cards than a PC. Some cards can get screwed up to the point that a PC can't do anything with them, at least that was the case with XP. Whenever I ran into that I'd just pop it into my Mac which would reformat and recover the card.
When I was still working where they used PCs people were constantly screwing up these cards and tossing them in the trash because the PC couldn't recover them. I'd pick them up, take them home and reformat them on my Mac for my own use.