(In the long run I'd guess we'd want to keep a little closer to the latest Ubuntu, though of course that requires someone to do the work.)
I am not not sure if we really want to keep up with Ubuntu patches, as long as we have no problems. It would perhaps make sense to do so, but we have not got a dedicated sysadmin.
Okay, I was wondering that (that's why I qualified my guess). mp3splt or no mp3splt, if Ubuntu 6.x is no longer being supported (which I don't know for a fact), then the system is fragile against e.g., security holes, which tend to rear their head at inconvenient junctures and consume annoying amounts of time to deal with, unless the OS can be expected to provide convenient and timely updates for such things. Which Ubuntu definitely does, for whatever versions of Ubuntu they're paying that kind of attention to.
So despite the fact that none of this is gonna be news to you, I'd say now's the time to think about the bigger-picture problem pretty carefully (if you haven't already), precisely because it isn't hurting right now.
I would be happy to volunteer some of my sysadmin-time -- including doing a significant upgrade of the OS, if we can plan it well enough that we're comfortable -- starting in a couple weeks, when midterm exams and papers are behind me. Would you be open to that?