I've only recently become a profitable player. I was breaking even at 2NL a few weeks ago and losing a few weeks before that, so I haven't had the chance to win enough to warrant withdrawing yet. I'm not planning to withdraw anything until I get to at least 10NL. After that, I'll probably withdraw a small amount of my profits (like 20%) and leave most of my winnings towards my bankroll, so that I can continue improving and never be stuck at the same level for too long.