I thought that I must be tricking myself, surely there was something I was forgetting or some loophole in my formulation of the problem that I was accidentally exploiting.
It turns out that I do a great many fun things, and I enjoy them as much as or sometimes even more than most people, but I never do them for the fun of it. It always comes down to a consideration of social bonding, or occasionally just loosening up my mind. This is the kind of productive play that Ben Goertzel describes. When I make decisions, fun is just never a primary factor at all in my mind. It's a side effect.
As my friend who asked me the original question pointed out, this is not even remotely normal. However, I wouldn't have it any other way. This is not the defense of some stressed out workaholic who insists that they are happy either. Living my life without fun as a goal allows me to constantly choose only purposeful activities that build up me and the people around me, allowing me to do an enormous amount of good in the world. Furthermore, while my goal is to do good, not have fun, a side effect of this mentality is that I have tons of fun. Knowing that you are always doing your best assessment of what you ideally should be doing ensures that you never have to worry about what you are passing up to do it. You can take the experience as it comes and really have fun with it. Furthermore, after a fun night, there's no regret. You spent it in a completely productive way and often had a great time doing so. Since it allows you to improve the general conditions of your world and abilities of your self, it opens up opportunities to have great times that wouldn't otherwise be available. I've done so many incredible things with friends and been able to participate in so many fun things because of it (like Academic Bowl, for a recent example).
As a side note, I'm now even more eager to read Eliezer's posts on fun theory when I get the chance!