Well it's all free advertising, so imagine one year earning them $50M from a $6-7M investment that year. Now imagine the fact that Lance and the USPS team has won 5 in a row, granted the middle 3 wins probably didn't garner as much exposure, but it's still a very big chunk of change.

Every Suburu commercial with Lance wearing his jersey is free advertising for USPS.
Every Coke and Comcast commercial is the same.
Every Trek 5xxx or TT bike sold by Trek up until recently in team colors is free advertising.
Imagine the dollar value of having your companies logo on the front page of Sports Illustrated a couple of times.

The list goes on, I just can't see USPS sponsorship as being a bad thing here in a financial sense. Sadly though most of that sponsorship rests on Lance's shoulders, the day he retires will probably be the day that most of the USPS cycling team sponsors announce they are also leaving as soon as contracts are up.

Andrew