About a year ago, I reviewed the update history on my main office PC. It was placed in service in June 2006 and runs XP Pro. I occasionally check the update history just to… Oh I don’t know, boredom, curiosity. A year ago after 40 months in service the answer is 380. If it had been older the number would have been even more since this one was commissioned after the release of SP1!
Today just 1 year later the count is 520 (512 successful, 6 failed, 2 skipped?).
UPDATE (10/18/2010): That was before the most recent “Update Tuesday” October 12th. The count is now up to 536!!!