Bruce Schneier, well known security expert and CTO of Counterpane Security, has a letter in the New York Times about the dilemma faced by CIO who run large numbers of Microsoft machines: there are too many patches and they can't be installed automatically because they often break, and yet if you don't, you're vulnerable to worms like Slammer.
I was having lunch this week with the CIO of a company you've all heard of. He's responsible for thousands of machines and they've had a policy of selectively installing patches after testing them for compatibility and effectiveness (i.e. doing Microsoft's QA work for them). Slammer hit them hard, in a matter of minutes. Now he's rethinking that and wondering if its not better to automatically install the patches and live with the clean-up problems that will inevitably result. This isn't some theoretical discussion. Its critical to the enterprise. If Slammer had hit at the end of a quarter, it would have had devastating consequences to sales at many companies. Yet, the cost of patching is inordinately high. No good choices here.