All through 2009, 2010, 2011: Bad .Net patches
Over and over again, we saw botched .Net patches -- some refused to install, others left .Net dead, others clobbered programs that relied on .Net. It started in January 2009 with a patch that claimed to push .Net Framework 3.5 to Service Pack 1, but didn't.
Another patch, in March 2009, also identified as .Net Framework 3.5 SP1, installed .Net Framework 2.0 SP2 and .Net Framework 3.0 SP2 as well. It was an unholy mess that had us going in circles for months.
We saw many more .Net patching problems in 2010 and 2011, all compliments of automatic update.