Like most of the replies on this thread, I am not in favor of DL's restriction of a PM upgrade on L-class fares. If there is a seat available prior to departure that would otherwise remain empty, why not give it to a PM? When I wrote to DL's Customer Service about this, their response was "to allow the use of minimum mile upgrade certificates in conjunction with our lowest fares is simply not practical from a business standpoint. To remain profitable, we must make every effort to make seats available for those customers who are willing to pay a higher fare for first-class travel." That doesn't answer my question on why PMs can't upgrade on an L-fare if there are seats in F prior to departure. I am a Million Miler and have been Royal Medallion and Platinum Medallion for the past 6 years, why can't I and other PMs get a break? As a result, I have been flying CO 60% of the time now.