Frequent Flier Ticket Availability

Recent research by Ed Perkins at Smarter Travel and Scott McCartney with the Wall Street Journal generally found that, in order, the best airlines for snagging frequent flier seats were:
American – good
United – good
Continental – fair
Northwest – fair
US Air – poor
Delta – none
We’ve recently had fairly good luck with United and American, but haven’t tried any of the other airlines lately.
(The Wall St. Journal original article above requires a paid on-line subscription, but a forum discussing the article is available here for free.)

ADDENDUM: Just tonight, after writing the above, we're trying to book a frequent flier ticket for next Thursday (a week away; domestic). We can't even GET INTO US Air's award booking site, while we found several flights available on United. Nuf said.