It all comes down to what dollar value you mentally assign to your favorite award. Most people decide how much a mile is worth by dividing the number of miles required into the dollar value of their favorite award.

I've never been one to refuse an upgrade, but am a dyed-in-the-wool free-travel redeemer (the kind who wants to try to use awards to see as much of the world as possible). The U.S.-to-Asia free coach RT is my valuation benchmark (currently around 1.5 cents a mile). Other favorite redemptions include September in Alaska on 25K miles, intra-Micronesia awards on CO for 25K, and intra-SE Asia on TG or SQ through UA at 20K. Stopovers and open jaws also are a big part of the strategy, and I really like being able to use miles on obscure monopoly routes where paid tickets are very costly.

But many people go for the upgrades, and after a few long rides in back on some planes I can start to see why - especially if you're very limited on annual vacation time but have plenty of miles.

You'll find the whole range of people on FT, though.