Other than the option to get larger storage.
That's hardly an "update". It's a different configuration option, it's not like the Mac Pro changed itself or in any hardware way - i.e. my Mac Pro from before them offering 750GB drives can handle the 750GB drives anyway.
As for people talking about silent revisions - yes, these do happen, meaning that if you got a September Mac Pro, it may not be exactly the same as one from December. They are, however,
essentially the same - the difference may be as simple as a different part being used due to supply problems. The machine will function exactly the same and you will suffer no ill effect from the alteration. Somebody mentioned the quiet revisions on the MBP to fix problems - yes, they did happen, but the product line itself didn't change. It's not important, and I dare say even Apple themselves are going to be able to differentiate on any basis other than the build week.
