The only two occasions where I've redeemed mileage have been as follows:
(1) To upgrade CHAcltLAXcltCHA on US (having been only a "DM4" at the time).
(2) For a trip to this past year's Scott Tournament of Hearts, ATLyyzYSByyzATL (Aéroplan miles can't be used for upgrades, and when looking at a US$500 fare v. 15,000 miles, it's kind of a no-brainer...)