I'm not intimately familiar with the workings of travel reservations systems, but I think some of them must have these automated functions built in. I've started having my corporate travel agent (AMEX travel) request upgrades for me with their computer system, and my experience has been *very* good with what I think is a much better chance of success at upgrades. I still usually check to make sure, but I think the computer is requesting exactly at 72 hours in advance.

Just to stick up for the computers here, and I don't know if this is the case on other airlines, what happens on Delta anyway is that FC is completely full sometimes and they have even closed the waiting list, so even if an upgrade is requested, there's no way of showing it has been requested if you didn't get upgraded or waitlisted. This happens a lot on certain flights (ATL-DCA in particular in my experience).