4. Business Application Users: Yes, a lengthy list of server applications from Oracle, IBM, etc., run on Linux. But consumers who run mainstream accounting, financial and other desktop applications could be out of luck with Ubuntu. Also, many hosted Web conferencing services only work with Windows.
3. Software Drivers/Printer Support: This is a big issue. Many consumer printers and other peripherals simply don't support Linux. This is changing, gradually, because companies like HP truly believe in Linux. But in the vast majority of cases, driver support arrives first on Windows, second/sometimes on Mac OS and third/if ever of Linux.
2. Windows Gamers: This isn't an issue in our house. Our kids live on our Xbox 360 and typically don't have much interest in Windows-based computer games. Yes, Linux supports a wealth of games. But for true PC gaming, your best bet -- by far -- remains Windows.
1. iTunes: My son, a third-grader, can't live without iTunes. When he uses our Windows PC, it's typically to manage songs and move tunes between the PC and his iPod. If anyone has found a way to make iTunes work with Ubuntu, I'm all ears. In the meantime, my son continues to live on our Windows system.