If it aint broke, don't fix it. I live by that and my computer rarely ever has problems.
ATI is notorious for bad drivers and slow releases, it's really unfortunate because they make very good hardware, but it's useless without good drivers.
MS is notorious for breaking more than they fix, but it really depends on the customer. If you don't
need one of the fixes supplied by them, simply don't install the update and you won't introduce instability. Most of the bug fixes MS implements are only really going to affect corporate customers not the home consumer. Most of the "features" MS adds are really just new bugs.
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