1. Overall consistency: For a Microsoft product, Windows 7 is quite refined. But it still suffers from needless inconsistency. Why do most of its tools place menus on the left, while Internet Explorer 8 and the help system shove them over to the opposite end? Does the new media-sharing feature (HomeGroup) have zero, one, or two capital letters? Why does Office 2007's Ribbon interface show up only in Paint and WordPad?
2. The names of things: Too often, Microsoft's naming decisions confuse rather than clarify. 'User Account Control' has nothing to do with the feature it supposedly describes; 'Action Center' sounds like Ron Burgundy's local TV newscast. And an OS that already has a feature called Device Manager shouldn't call a new feature 'Devices and Printers'.
3. Windows Update: The operating system's built-in patching capability is essential. But Windows Update is also the OS's most irritating carryover feature. Tell it to download and install everything without your further intervention (as Microsoft recommends), and it may still insist on rebooting when you are in the middle of important work--or deny you access to your computer altogether while it installs updates.
4. Search: Windows 7's Federated Search lets you add external sources like Flickr and YouTube to Windows Explorer searches. But the OS doesn't help you find those sources and doesn't mention Federated Search in its help system.
5. Help: Help...needs help. Some sections target nerdy command-line aficionados; others address clueless newbies. Few sections focus on intelligent-but-busy users of intermediate experience.
6. Flip3D: Press Windows-Tab, and you get Vista's fancy 3D task switcher, which pointlessly requires you to cycle through tasks one by one. This duplicates the functionality of Alt-Tab instead of enabling you to get to any task in a couple of clicks, as Apple's similar Exposé does.