Played a campaign where you could chose (in advance) either to roll the die or take 'low average' (ie, 3 on d6, 4 on d8). Very few people ever took the GM up on that one.
Next game, different GM, option to roll or take 'high average' (4 on d6, 5 on d8). Lots more people took him up on that, including me a few times.
Me personally, When I GM, I take a hard look at the PCs every couple of levels. If they are below average hit points, I'll cut them a break the next time they roll hp, by ensuring that their new roll is not below average for the die. Heck, for one guy who ended up way below average at 4th level (usually the first spot I really worry about it), I just grabbed the d8 that he'd rolled a '1' on and flipped it to '8'.
But then, I'm one of those people who likes high point buys too.