Actually, Comicwoman, it seems that a majority of the flyertalkers use their miles for upgrades as opposed to award tickets.

There are some HUGE differences in the mileage levels required for getting upgrade certificates. From the posts here:

AA - 30,000 (maybe 35,000) miles for 8 500 mile certs.
UA - 30,000 miles for 8 500 mile certs.
DL - 10,000 miles for 4 800 mile certs.
US - 10,000 miles (8000 for Preferred) for 4 800 mile certs. (Can claim individual certs. for 2500 miles each or 2000 miles for Preferred)
AC - 28,000 miles (for SuperElite) for 8 certs. (each good for one-way trip of any distance) - Yes, BlondeBomber, this is a deal!

Interstingly, it seems that all of the airlines are charging about $40 for purchased segment upgrades for non-elites (about $30 for elites). UA is charging $50/cert. for non-elites. And the UA and AA certs. are only for 500 miles!

Also, if I understand Jimboliguy's post, a R/T upgrade on AA (any fare) is 30,000 miles in the US. More than claiming a free coach ticket. Am I missing something - that doesn't make a lot of sense.