Flew LH on L-class ticket twice in the last few days (ORD-MUC and FRA-MUC), agents in ORD and FRA would not even consider accepting a paper UA-SWU to upgrade the flights. Agent in Chicago even pointed to "L" on my ticket and said "see that? That means 'low class'!") Figured it wouldn't hurt to ask, and I didn't really expect LH to bend a rule, so I wasn't too disappointed.
I did get a view of the empty biz-class seats from my economy seat.
