@ mooster
Actually that would be a wise idea. Assuming that your parents are the type of user that neither cares or knows about how PCs work they'd (or in case you are their helpdesk, you too) roughly have 3 advantages:
1) better safety, which well.. needs no explanation. Compared to the old win98 days it's a lot harder to get a virus, although certainly not impossible. I've gotten PCs with over 100 virusses from family before, I'm pretty sure it'll never get that far anymore with W7. I think the average user would actually have to do some seriously wrong stuff to just get one now.
2) great stability. I never really blamed Windows much for crashing, since it's usually the fault of bad hardware/drivers, but I'm happy to say that drivers will not bring down the entire OS anymore when they crash. Once again, it's not impossible, but instead of BSODing Windows will now just report a driver crash and continue to work. I generally prefer stable drivers so I never have many crashes at all, but I had one in an earlier beta of W7. Windows just reported the crash and kept on working. It will not solve bad drivers, but atleast it won't crash the OS and thus lose your newly typed Word document anymore either, which should be a big plus for most users.
3) no more annoying UAC. If you ever used Vista then you know how annoying UAC can be. In the end most people switched it off completely just to get rid of those horrible prompts, thus removing all of the protection too. In W7 you can have UAC on and not get bothered by those messages much. They are still there, many times they should be, sometimes in my opinion I shouldn't have gotten a prompt (for instance every time I start CCleaner or my Defrag program I get a prompt) but you can fiddle around with UAC settings to change that to a setting where you get as much protection possible with as minimal annoyancies.