There are some rumours circulating about problems with the latest round of security updates. The Security response centre have posted about it. So has Roger Halbheer our Chief Security Advisor for Europe. Now you can say “They would say that, I’m going to take my chances with whatever security loopholes were being closed” or you can say “The reports of problems are of dubious provenance, Microsoft probably wouldn’t post outright lies” etc. Given how quickly our patches get reverse engineered into exploits I’d see a lot more risk in not having them than something which screws up coming out of one of the product groups , as the MSRC post says "it appears they’re saying that our security updates are making permission changes in the registry” and “We’ve conducted a comprehensive review [which] has shown that none of these updates make any changes to the permissions in the registry”
And if, you do think an update has broken your system, don’t suffer in silence I’m told Microsoft support will always take the call from someone in that position even if they don’t have a support contract.