FWIW the update to Flash Player 11 has been notorious for issues. I'm still on version 10.
The last Windows update to actually cause me issues was back when IE8 first came out, generally WU isn't the arch-villain it's often made out to be.
Of course the ideal is to have a dedicated DAW machine that is hermetically sealed in foil, but many of us have a single set-up where some general usage is unavoidable. If I was running professional studio services then the machines involved with that wouldn't be on-line but for many of us there is a happy medium between excellent DAW performance and general use computing.
Looking back at the reliability monitor since January I have had a total of 3 application hangs, and bear in mind I've been beta testing a few products in that time, otherwise my reliability is a straight line at the max. I've seen studio machines that are isolated from the web that frankly I wouldn't use because of the mess of issues that are unattended leading to all sorts of unwanted behaviour. A good policy to keep a secure, well-found and maintained machine is a more important consideration than merely whether it is connected to the internet or not.
Frankly I've got better things to do than check the specifics of each Windows update when they are offered so I choose all the important one offered generally and roll-back if any issues arise. It's far quicker than finding out what each one is for.
By keeping my drivers and system updated my computer is faster and more efficient now than it was when I got it, yes, sure it would be working still like the day I got it had I not updated it since, but trust me it's working a whole bunch better than it did, even purely for DAW use, being as updating since then has led to a 2 ms reduction in RTL over it's original configuration.
There are no rules, but there is plenty of good guidance to be had.