Like ANY major changes, its a pretty smooth transition for those that are savvy, and not so much for everyone else. The average user won't notice much difference except for the user interface, but 7 *is* an improvement functionally from all before.
That said, it doesn't do everything. .zip files have never opened natively in windows, as stupid as that is, but its pretty easy to find a program that opens compressed files. WinRar is my program of choice, and it opens any kind of compressed file you can imagine.
So, what most people judge are the user interface, which is arguably better, or arguably not, depending on how comfortable you are with computers. It seemed to me like grumpy is pretty savvy, judging by knowing that he could stick the old HD in a spare bay, so there's no reason to tell him not to switch.