2 things that I wish UA would allow based on Mileage Plus number:

1) Access to existing reservations, no matter how they were booked (Travel Agent, UA Cnxn, ITN, etc.) based simply on the fact that my mileage plus number is associated with the PNR.

2) Flight-Paging automatically added to any flight that I'm travelling on without manually adding or updating it.

It doesn't seem like these 2 things would be that difficult to do since UA knows who I am and should be able to link all of this info together under my MP number instead of individual PNR's.