Some people have already found that they are having issues with anti virus programs installing, and/or behaving on Windows 10. I would have expected that myself. Most anti virus software runs at the system level and is very tightly bound to what the OS is doing. This same issue cropped up with Windows 7, even after the final release. Some companies were quicker to come out with updated/upgraded software than others. Another big problem I suspect we will see is any multi function printer that doesn't have native driver support in Windows. When Windows 7 was release many people found they could print but not scan or copy or fax, (kinda cuts the muti out of the function). If you have MF printer or AV issues, do without or go back to 8.1 if it's critical to you.