Of course they did, everyone "saves" them to use on a overseas trip. Then when it comes down to it, they weight if the upgrade is worth the $1,000 higher fare required to pay for it.

CO have VERY few passengers using their BF upgrade process too. It's expensive. But in my opinion CO is more expensive. With DL SWU you book in M or above...with CO you book however you want but then pay a fee that equals going to M or above PLUS use miles, keeping in mind you probably won't get the upgrade on half your trip if you are based on the West Coast unless you've booked in a higher fare bucket anyways.