For those of us who use computers in the lab...
Windows 7 is abso-fraggin'-lutely unacceptable.
OK, so maybe they've got it working for typical office users to do their word processing and pr0n browsing.
But! Some of us need to talk to external devices. Like, over asynchronous serial ports.
One of my clients uses Windows machines in the lab. The ones running XP work fine. The new ones with Windows 7? There are various problems with COM port handling... ranging from the API being intermittently broken (can't always set the Baud rate) to a can't-be-disabled Feature randomly stealing characters on the assumption that any COM port simply must be used to connect a serial mouse.
And the latest development: one guy there got a shiny new Core i7 machine. Windows 7 consistently recognizes the built-in COM port, and could be persuaded to install the drivers for a USB serial converter... but, depending on its mood when it boots up, it may (around 10% probability) or may not actually deign to send and receive data on those ports. So, he's stuck with having an old XP laptop alongside the new machine, just to communicate with the embedded systems he's working on.