It'll let you vote but it doesn't count it. It's based on ip address. I tried two different computers in the shop and I could only vote once. The second computer said "your vote has already been counted" indicating its not based on cookies.
EDIT: i'm wrong... it may be cookie based. i just logged into ubuntu and it let me vote. someone must've voted on the other computer in the shop (they're not supposed to be on drudge! lol).