Pepsi did this in Australia a few months ago, gave away bucket loads of 15GB iPods. Don't bother entering between midnight and 6AM everyone thinks that's the time of day with the least entries so they stay up all night to win. The few people I know who did win entered mid morning when kids are at school and most people are busy at work.
I entered about 20 or 30 times didn't win a thing.
I now drink Coke.