I got some emails from other participants of KDDCup2012 about what kind of approach I am using. According to the rules, I am not allowed to disclose information to other teams by email but only to the public (e.g. this forum)...

All my submissions in track1 and track2 are made with the Factorization Machine model (FM). My best leaderboard score 0.41509 on track1 is a single FM model (no ensemble).