There's a save game bug in Minigore Episode 3.7 - Don't update and wait for a fixed version!
If you already updated:
1. You won't lose your In-App Purchase characters!
2. Also it should be possible to recover your unlocked characters through OpenFeint achievements.
3. Normal, Hard and Insane difficulties are already unlocked on first playthrough on Minigore HD - we'll add that change iPhone/iPod version so you don't have to grind through earlier difficulties.
4. As a final change we might give for example 20 000 kills at the start of the game that you can spend on any character.