It is a standard offer for many airline programs. I traded in 500 miles from my USAir account earlier this year for 5 magazine subscriptions, so that was a good deal. I also did the same for my wife's account. We can't complain since this was a great bargain - 10 subscriptions for 1000 useless miles.

When I receive the offer for accounts that have several thousand miles that I might use some day, then I toss the offer. No downside, no commitment.