Leaving Under the Gun

[Penguinfan]

Out of curiosity, is it commonly considered bad manners to leave the game just before the big blind gets to you? I can't say I pay alot of attention to this because I generally leave an on-line table when I get too tired to pay attention or the kids need something, or whatever, but I was watching the chatbox as some guy was all pissed off about a player leaving before posting the next round of blinds and 2 other players typed in agreement with him. I thought about it and kinda feel like when I sit down I post a blind or I wait till the big blind gets to me then I post, but I post before ever seeing any cards so I have paid for the next 8 hands after posting the BB and SB in my opinion, so if I want to see those 8 hands I have payed for then I should be able to and then leave if I want. Am I way off here, is there some sort of protocol I don't know about?