This week, CU4 for SQL Server 2008 SP1 was quietly slipped some updated files, referencing a KB article that does not yet exist. I wrote plenty about it here:
The biggest danger, I feel, is that users who have tested CU4 (2734) in their labs may tell their deployment team to go download CU4 from support.microsoft.com, and deploy it to their production environment. But when they get there, they could very easily choose to download the "updated" version (2740). I don't think I have to explain how many ways this could end badly.