A link from Kevin Kelly's Cool Tools website - Rulesofthumb.org. Like any rule of thumb it is not apparently obvious how accurate these are, but in my experience this is a particularly good rule of thumb:
Inviting more than 25 percent of the guests for a university dinner party from the economics department ruins the conversation.I have no idea if the next one is true, but if it is then using a service such as StickK could be a particularly profitable investment for executives:
Fat corporate executives earn less money. Each pound you are overweight costs you about $2,000 a year in salary.