The only time I was able to buy an international ticket and knew at the time of purchase (7 days before departure) that I had a great shot at an op-up was an itinerary in early October, 2009 with the return leg DUB-ATL-DCA. The seat map on delta.com showed no seats available for assignment in Y, with BE wide open; expertflyer.com showed L9. For whatever reason, the DL computer decided to keep selling cheap fares and oversell the flight.

When I got to DUB airport 4 hours before the flight, I got the happy news from the counter agent. Had a great flight too. Thought that pre-clearing immigration in DUB without clearing customs at the same place was a waste of time, since it ended up taking almost an hour in ATL between waiting for bags (our "Priority"-tagged bags came onto the belt last) and standing in the line waiting to see the customs inspector.

As far as who gets an op-up, JFK was (and may still be) notorious for giving op-ups to people without status. I witnessed this on a JFK-LHR flight a couple of years ago; I was on an L fare when I misconnected with the former morning departure; the SC concierge immediately booked me in full J on the evening flight. This was a holiday weekend, and Y was oversold. When I boarded with the BE group, there were maybe 15 of us. At the end of boarding, the rest of the BE seats filled up--there was a family of 6 who ended up in BE, along with a husband and wife who didn't seem to be frequent flyers of any airline, let alone DL (the wife burst into tears when she realized that she wouldn't be seated next to her husband, even though she was in 5B). It was hard to believe that there weren't 15 medallions of any status in Y.