Depends on the market. I use 15k UA for MCI-DEN on occasion, and 25k NW for MCI-DTW. Those are short, but expensive, trips. Oddly enough, award seats are usually available on those, even when the airfare is $400+.

For those awards, it's easy to calculate the redemption value in terms of real cash in pocket. 1.5 or 2 cents or whatever that I was really going to have to spend.

For some other awards, I don't even bother calculating a redemption value...I just do it because it sounds fun. Upgrading to Europe for example...what's that worth? I don't know...I probably wouldn't spend even $500 of my own cash to upgrade, so technically not even a penny a mile. (The airlines may ask a ten grand or a million dollars for that seat, but that doesn't matter: I wasn't going to pay that to begin with.) But I still get a kick out of those redemptions...