It's a great, bold step forward that now both Windows XP and Mac OS X take steps to hide the jumble of files, libraries, and registries that make the OS tick. Truly, for most users, even the most advanced, what's in there is of absolutely no consequence. As long as everything is working, the system files should just as well be invisible and inaccessible, just as the average driver need not know where the brake master cylinder is located. However, computers tend to have problems, and unlike a car, users will routinely install software that inserts its own files willy-nilly among system resources. That's like having your dashboard hula-dancer require a connection into your car's cooling system to wiggle properly. A bare, out of the box installation of your OS will usually run flawlessly. Any hardware issues that are likely to cause problems will usually manifest themselves pretty quickly. The problem is, our computers are constantly being changed around, both their hardware and software.
This is another case where by making the computer friendlier for newbies, we're actually missing out on a case where an experienced user might be missing out on important information. If, when installing anything, the process of these zillions of little files were made more explicit, two things would happen: first, it would open the door to more awareness of where problematic files are located, which would help in troubleshooting. Second, it would create a groundswell of revolt against lazy and irresponsible software and hardware vendors who, for example, demand root access to your machine when they really don't need it, or replace libraries with older versions, or any of the nasty things that crap software can do to your computer.
What we get instead is a layer of annoying pop-up messages warning us about all of the security threats we're making ourselves vulnerable to. They're like the boy who cried wolf. Novice users don't understand anyway, and all users end up on reflexively clicking OK so often that the warnings become meaningless.
The problem, in so many of these cases, is that the personal computer needs to be all things to all people. No matter who you are, your computer is pre-loaded with all sorts of capabilities and utilities that are useless to you. They add complexity, but don't serve you in any way. They have also been slowly evolving over decades, and every major OS retains a lot of legacy cruft that may or may not be necessary for your software to work. OS makers have done an admirable job of taking these aging battleships and bring them into the 21st century, but I think that a lot of the efforts at increasing ease-of-use have been misplaced. We don't need Clippy, we don't need Microsoft Bob, we don't need the retarded OS X dock or more wizards. We need a focus on easily-learnable, non-intuitive user interface features and tools to deal with the mass amounts of stuff we store on a modern computer.