I'm running a MacBook Pro, Mid 2010 model, that I recently upgraded to Mountain Lion. Around that time, or maybe shortly after, I began noticing some problems that I can only attribute to a general slowdown in accessing files on my hard drive. I have 8GB RAM, and rarely run out, so I don't think it's just a matter of paging vs not paging.
The evidence is reasonably convincing. For example, I'm a Java programmer and use NetBeans. The app I have configured takes over a minute on this machine to run, but only 30 seconds or so on a more-or-less identical setup on a much weaker machine: a late 2008 MacBook with only 4GB RAM. And what it's mostly doing is reading and processing several hundred files of various kinds.
So far, though, the evidence is entirely anecdotal. I'm looking for some kind of test I can run that will see whether my file system/HDD is performing as expected or whether it's something else entirely. Also something I could take to the Apple Store and say, "look this thing says there's a problem." Does such a thing exist?
Edit: another interesting difference. This Mac takes just shy of three minutes to reboot (that's desktop disappearing to desktop reappearing). The older MacBook I'm comparing against (also running 10.8.3) takes just over one minute.