Our giveaway was sort of similar, but a lot easier to enter - everyone got a weekly entry (random number - by clicking enter via their profile) but there would be bonus entries a few times a week too (with conditions, e.g., post on the forum today) it kept people coming back and the brand in mind throughout the whole year (we gave one away per month). It was a fun project - I coded it in Rails and put it in a sub domain.