I remember one of the market wizards making a comment about how foolish it is to have on too many correlated positions - which essentially acts as one huge position. So for me the ideal number of positions is 3. I put all my money in my top three trading ideas/themes - such as: (1) short commodities (2) short bonds and (3) long equities. I think by putting on any more positions is like stretching oneself too thin - it just makes it a lot harder to focus. Only if you're just scalping does having a lot of positions can make sense. BTW I don't think anything is "uncorrelated" in the markets but you get the idea.