If the pot reaches a certian amount (usually 30xBB), the next hand is played for double the stakes (5-10 is now played as 10-20). Also if a player wins two hands in a row it is a kill. There must be a flop to have a winning hand qualify.

When it is a kill, the small blind and big blind are the same (for 5-10, SB=2, BB=5) but the player that killed the pot posts an additonal "bigger" blind. For example, in a 5-10 game, SB=2, BB=5 and the player that killed posts 10 and the game is played as 10-20 until the player losses a hand.

Hope that helps out a little. I have not noticed many kill games on-line. I know the UB has a few of the running but not sure about other sites.