Allthough I have not flown UA recently they used to be excellent about upgrading US and all OA employees. One afternoon I was on an ID90 (before we had ID95's) DEN-LAX on the 744, when I checked in the agent said, "I'm sorry Mr ... First Class has checked in Full,. would you prefer the Upper or Lower Deck in Business". Just keep in mind their 735, 733, and 319's only have 8 F seats so highly unlikely getting upgraded on one of those but at least their 757's are still F24.
Also it is my understanding Zed Fares may be in the works !
Cheers
LGA777