I occasionally read about people running the permissions repair script just because, and I wonder how much of this has come as a result of the habits in the days where it did benefit to run utilities such as Norton Disk Doctor, TechTool, disk fragging utilities, etc.?
Anymore, the only real maintenance needed is handled automatically by the OS via daily launchd jobs (cron jobs on other Unix OSes), and this is generally simply in turning over log files, deleting old cache files, etc. Even without these things being run, chances are your applications would continue to run fine. Really the only preventative maintenance that I can think of running is security updates.
Does anybody disagree with my assessment and still feel like there is a point in running some of these utilities periodically?