I agree that it is possible to receive an upgrade at OLCI -- I have had it happen twice in the last few weeks.

For both of those flights, I originally had my United 1K number in the reservation. Each of those trips were flights that were originally booked an express flight..so there wasn't any real benefit to using the US acct vs. the UA account. (and I'm more worried about requalifying for UA status!)

My scheduled changed, and I ended up on mainline flights. Upon OLCI, I saw that there was the option to purchase an upgrade, and so I switched to my US number from UA. (am also gold on US). The button changed from purchase an upgrade to "complimentary upgrade available" (or something like that).

I know that the sequence above is certainly not optimal for maximizing my chance at an upgrade....just wanted to share that it is possible.