Both a tease and meaningless. If we've learned anything in the time GOG has been around, its that the amount of interest in a particular game as represented by the wishlist has no bearing whatsoever on whether or not we will ever see it here.
Yet still, when negotiating with people holding the rights to a game I bet it makes gogteam's life a bit easier when they show them the numbers. So while voting doesn't get you what you want, it might not be totally pointless.
Which reminds me there are local elections over here this week...
(edited for typos)
Except the wishlist is completely unscientific and cannot be considered a valid measure of interest by any stretch of the imagination. Any potential rights holder that looks at the list and sees entries like "All the fucktards that vote for this entry" would immediately disregard any other information that might come from it as complete bullshit. That being said, if the GOG guys spent a little time cleaning up the list and implementing some kind of control over it, whether through community intervention or a dedicated employee intervention, it might become a much more useful tool, but as it is now, it is a waste of time, other than as a means of stopping people from creating the ever popular "want game nao!" threads.