Winner is randomly selected from the list of registered miners.
Your node must have found at least one p2pool share in the last 48hrs to be included in the raffle draw.
If you win and you have no shares in the time window, you are skipped.
Fail count is automatically reset back to 0 after a successful win.
If you have shares in the main sidechain PPLNS window you are a "VIP".
Every other raffle round consists of only VIP miners, thus VIP miners have a greater change of winning.