On both of my recent intercontinental KLM flights (AMS-BKK and HKG-AMS) I was offered a paid upgrade to business class during OLCI. (EUR 224 on the outbound and something like EUR 330 on the inbound) In your experience, how often does this happen? I paid on the outbound as I found the extra fare reasonable, and stayed in economy on the inbound (and slept 8 hours non-stop on a packed flight!)
I also was happy to see that I received 125% miles on the upgraded flight.
Added: AMS - BKK was booked in K class, HKG - AMS in T class