There are a lot of things that can make for an enjoyable round on a mediocre course. A beautiful setting is one (Arrowhead, anyone?), but there are others. Great company, as was mentioned before, is huge. Another is scoring well. It may be weak to admit it, but I do tend to have a better day when I'm scoring well, or even just hitting some great shots. I saw Tom Doak's post, and from his perspective I can see that a poor course built on a good bit of property or a property with a nice view is an opportunity lost, but for a guy like me, the fact that the course might be cheap, for instance, might help make the round better! Throw in good beer choices from a pretty cart girl, and it seems like a nice day out. If the course is a great walk, then all the better.
I generally know the quality of course I'm heading off to play. Maybe my expectations change when I know the course isn't that good, and thus I'm more able to ignore its inadequacies. Maybe I'm just easy. Or cheap AND easy.