The code works fine (enough); that's why they will (now) ship nightlies of Win64 builds. The problem is two-fold: 1) They don't want their engineers to spend time fixing Win64 errors, and rely solely on people who care a lot about Win64 (thanks, m_kato!) to clean up after the "normal" people. 2) For some silly reason, they have nowhere near enough machines (and people to run them) to properly support development. This is even ignoring Win64 builds - multiple checkins will typically share an integration build, and checkins frequently has to stop to back out a bad change and wait for the machines to catch up to make sure the problem is fixed. They have a system (try servers) to fake-checkin to run the tests to make sure things are good - but due to resource constraints people are encouraged to reduce the coverage; heck, they have a "high score board" to shame the heavy users.