I gave such a system to my dad (very non-tech savvy)... It was behind a router, had a hosts file from hell, and I showed him jotti.org
for any file he downloaded.
It uses Firefox... bout the only thing he does is browse the web... this machine is an old K6 500, it is in his shed/barn in the backyard... he looks up stuff he is working on out there... google images, wiki, etc... nothing heavy... he realizes it is an old machine and he knows if something don't work he should truck inside and use the AMD Athlon X3 450 I built him.
It also runs XP SP2 with all my usual tweaks... It's been about 6 months since he called me up with a question. It was the newer machine, he was on a government site that checked his version of Adobe Reader (it was 7, they wanted 10 or something).... I showed him howto bypass the check(was quite simple) and download the pdf... surprise surprise... it WORKED in version 7
He understands the machine in the shed is old, his main machine just plain works, he doesn't like the smaller screens on laptops, so i put the old one out in the shed with wireless and an old 19" tube monitor(man that thing is HUGE). Older people that are less tech savvy seem to have more patience with older stuff... It seems to be the younger crowd who wants all the "pretty" new toys that a newer machine provides.
I let my dad use a netbook(external monitor/keys/mouse) with 7 on it for a week or so... He asked me... "I see it looks different, but why do I need it?", I of course told him he didn't
Most people will never notice the tweaks, missing services, or tasks(that AINT running)... Even the most non-tech savvy person can be taught to run SpyBot once a week when they walk away from the machine, or manually scan a newly downloaded file.
People are actually getting more and more "dumbed down" when it comes to computers because of all this letting the (in comparison) stupid computer take care of things for them... when something does go wrong, they don't have any more of a clue then the computer does