No offense but that seems pretty lame. Free entrance and drinks to a party in Amsterdam. I think anybody who can be a part of your top 25 can easily afford to pay the entrance and drinks. I just don't see this promotion being any help to you, unless you are marketing to dutch webmasters only.
Instead why not have one top prize and offer free entrance and drinks to every webmaster that promotes you. That's a MUCH Better idea. That way you'll encourage everyone nearby to check out your party and you'll have people pushing hard to win that big prize.
Just my
