I very rarely play Cash games On-line, but I will stick to the 1% buy-in Limit for any Tournament. On
pokerstars This ranges up to $5.50 Tournaments, because I have over $600 BR Balance, but in general I will buy-in for much less on single table games, Why? because I do not play Poker On-line to make money, I Play Poker because I want to experience the Roller Coaster Ride of Emotions, and just enjoy playing the Game.
Live games however are a different Story, but at least I can see the colour of their eyes of the people I am up against, and to me that is very important if I want to get a read on my opponents.