There is a limit of 50 birdmiles per day.
To earn 1000 Mileage Plus miles you would need 20,000 birdmiles which by my calculations would take you about 400 days to earn.

Assuming 1 birdmile per message read this means you would have had 20,000 views of the author's pages. At a standard advertising rate of $3 per thousand views the author would have earned $60.

The value of 1000 miles is, by my claculations worth about $20 leaving a tidy profit of $40 for the author.

Not worth it IMHO.

cheers Peter