A colleague of mine talks about a situation where everyone started being really, really conservative about code changes because they were afraid more radical changes would jeopardize their annual bonus. Slowly but surely, code quality eroded, bug counts went up, and the code became brittle.

So--if the bonus is little, it may be fine to divide it equally. Yet if it's as large as half-a-month's salary or more per person, this is a dangerous bonus. I'd rather the money get re-distributed as a raise and get paid out slowly. Then I'd recommend not having bonuses at all--we're trying to help people feel safe enough to be creative, to take risks, and to radically improve the ways in which they do their work. So get money out of the equation.

I think if the team were functioning beautifully, I'd divide the sum up and give everyone an equal amount.

If the team were functioning anything less than like clockwork together, I'd have some sort of team building day out with the money and try to integrate those who might not gel so well in the office. If letting people chill together outside the office helps communication in the office then it's all money well spent and people generelly enjoy these days (once they get over not getting the cash!!) :)

I would divide the bonus equally. There simply isn't any good measure of what should be rewarded in the team.

If someone isn't pulling their part of the team's weight, there are better ways to address this than using economic rewards or punishment.

If any team member is officially partially committed to the team, they get a corresponding part of the bonus.

If the team decides the bonus-model, hopefully they will arrive at the same conclusion :)

Another way could be to give each team member a shard of the same size, which she/he is free to give to any other of the team member (i.e. Das perfekte Dinner system).