What about "best value" rewards (ie not necessarily the longest distance/highest class, but something else you value)?

I used 40,000 AC miles last Christmas to fly home Business Class within Canada - a 5 hour flight in each direction, plus a long snow delay on the ground, during the stressed-out, jam-packed Christmas season. An economy ticket is 25,000 points, so a 40,000 point business class seat in those circumstances was a good deal. I never would have purchased a business class seat. Air Canada got rid of most blackout periods last year, so you can use points at Christmas. I've already got my business class seat booked for Christmas 2003.

I haven't tried it yet, but I've heard that another good value is WT+ upgrade to Club World (NA-Europe), using a discounted WT+ class fare (about 25,000 miles plus a ticket costing about $1350 Cdn).