play until you have all the money! just kidding, but seriously, I dont understand the double up and leave idea. If you only ever double up and leave, even if you playing good and the rest of the table isn't, you keep yourself from getting into big pots with bad players. I look at it as if something goes wrong and I lose, I only really lost my origonal buy in, but I have a chance to win a LOT. I think about it as a tournament buy in. I payed this much to play, and its not really my money until I leave the table with it all in tact. If I get to the point where nobody at the table can hurt my stack, and I'm way over the max buy in, I can play all day at one table without worry of anything too terrible happining. And when I get wore out and finally quit I gave a steriod boost to my roll with only ever risking my origonal buy in.
On the other hand if your losing consistantly you should call it a day. Me and my brother have had some good arguements about this. I tell him what I'm telling you, some times its just not your day. Doesn't matter if your the favorite every time the money goes in yet you lose because of dumb luck, just walk away and try again tomorrow. He never listens and always takes huge hits to his roll. His mentality(which I understand his thinking, just disagree) is that if hes playing good even through the beats, and continueing to get his money in with the best hand, theres no reason to quit, it should average out eventually. The probablem is that it doesn't. He just suffers beat after beat after beat until he wants to scream, and ends up losing a lot of his money.