Wouldn't it be nice to have cross-site bounties?
After all, if I am a developer I am likely to have points on SO, and not many on SF, and vice-versa.
I think probably everyone would benefit from such a feature.
Update: I agree that cross-site reputation, privileges or many other things would be bad. Bounties however, are a completely different topic. You "pay" some earned rep to the person that will answer a question that isn't get an answer otherwise. You are skilled in a field, and you need help in another field: that's the founding principle of the entire economic system in general.
Cross-site privileges would mean awarding powers in a field to people who do not have earned it in that filed, and that is bad.
Cross-site bounties means allowing you to sell your milk to buy some meat.