After a quick visit to the websites, I came up with the following (though won't swear for it's accuracy)

Sat Stay allowed for Coach:
UA, AA - Not Allowed
Delta, Northwest - Appears to be allowed
US AIR - Only booking codes YBMUHQ allowed for coach

Dates of Offer:
UA, AA, US Air - Now to 9/30
Delta, NW - To Oct 7

Registration Dates
All by 9/30

Number of freebies you can earn
All limit it to 2

Black out dates
US Air - Didn't find them, though they say they have them, and didn't look all that hard, all the rest - 54 days between November this year and 12/31/04

Fares Allowed (listing coach only)
UAL - All, but no Saturday Stay allowed
AA - not EGISTUWZ
Delta - not LUT
US Air - Has to be YBMUHQ that do not require a Saturday stay (the assumption is you can stay a Saturday, but the fare can't require it)

Booking class of free ticket
Delta - E
NW - K

[This message has been edited by cordelli (edited 06-10-2003).]