UA allows 50ponds on Domestic and 70pounds on International flights.
I was told by few friends that were 1K - theat they were charged $25 for their bags exceeding 50lb limit.
One time I did the curb side check in and the Skycap guy said my bag was over weight (by 5pounds - which was true) - but he is going to let it go

He did get a nice tip though