Windows 7 is the one of the best OS we had after Vista but maximum peoples who are upgrading from Windows XP to Windows 7 has the problem of application compatibility. So Microsoft has now given the list of Windows 7 compatible applications here: http://www.microsoft.com/windows/compatibility/windows-7/en-us/default.aspx
So go ahead and check out for your application which you are running the most. On this above given URL Microsoft tried to takeover the every application from Music apps. to CRM all the applications compatibility they have given.