My personal opinion is that it really doesn't matter. I'm of the opinion that if you've got a PC with a really low number of HP, the GM should make adjustments so that you don't get knocked off the fist time you get into a fight. I know that nowadays it's pretty commonplace for comic characters to die, but back in the day, you just didn't see characters getting whacked. 

I don't think the GM's job is to try his best to kill the PCs. I think my job is to tell a story that keeps my player's interest, allows them to develop their characters, and provides them with interesting challenges. Not see how many of them I can kill off this game session. I might be in the minority on this, but I think that's the way I think the game should be run. I'll get down off my soap box now.

Well, technically the minimum would be 1 if you look at the rounding up factor... but realistically, I have to go with the "depends on the angle of your campaign" stance. If you are playing more of a Batmanish type hero game, a lesser number of hit points are needed. If your typical villains are worthy of Spiderman or greater, more is needed. It really depends on the focus of your tastes in the genre and your needs.

I agree with folks who say that there shouldn't be a minimum, but in a game where a single attack can do 20pts + a damage bonus, you really can have too few hit points on characters.  If a player wants to play the character, that's fine, but I'm normally willing to let them redo the character from the start.