User Account Control is easily one of the most hated features of Windows Vista, according to readers. The seemingly endless stream of UAC pop-ups, asking you to confirm this action or that action, just get in the way (and aren't particularly zippy, given the screen redraw). Others don't mind UAC, but there's no doubt it's a controversial "feature" of the OS.
At the RSA 2008 confab in San Francisco, Microsoft admitted that UAC was designed, in fact, to annoy. Microsoft's David Cross came out and said so: "The reason we put UAC into the platform was to annoy users. I'm serious," said Cross.