You might think this is a joke, but I am serious:
Let Acrobat users sign up for collecting miles while using Adobe products.

How?
The difference between two mouse points after moving the mouse in a given time interval can be tracked without noticeable performance loss and saved as accumulated distances.
Adobe products like Acrobat could track the mouse movements and maybe even display a counter in the UI with the logo of the airline that is sponsoring the program.
Why would we want to offer this service? We could charge the airlines on a per user usage base.

There are some technical details that need to be looked at: Shall 1 "mouse mile" translate to 1 airline frequent flier mile? We might have to come up with a reasonable ratio. The mileage program should probably also max out at, let's say 5000 miles.
Another question is: How do you detect fraud?

If you are interested in some answers and more details please have a look at the attached patent application that I filed in 2005. Yes, I filed a patent for earning miles by using software products and it has not been rejected yet.