A very common misconception that I am hearing regarding Windows 7 is that Microsoft has removed all of the problems that Windows Vista had caused with application compatibility. While it is true that certain features of Windows 7 have been improved/tweaked, such as User Access Control (UAC), there will still be many applications that worked without problems on Windows XP but will experience issues when executed on Windows 7.
The difference between Windows XP and Windows Vista was huge, and since the release of Windows Vista some three years have passed; Windows 7 has evolved even further and incorporated many more changes. A good portion of the compatibility problems can be fixed using various methods, but the fact remains that migrating from Windows XP to Windows 7 will not be a walk in the park.
Microsoft has up on its website a list of applications, along with their exact version numbers, that have been approved (by the developers, not Microsoft) for running correctly and as expected on Windows 7, check it out here: https://winqual.microsoft.com/member/SoftwareLogo/windows7list.aspx
If you are planning on migrating to Windows 7 then the best thing you can do right now is to consult the list and start talking to your application vendors in order to find out which of your applications are going to have problems when run on Windows 7. Something I often saw when Windows Vista migration projects were planned is that application compatibility testing was often started too late in the project, or was not assigned enough resources simply because the problem was underestimated. This caused delays, sometimes substantial, in the deployment of the operating system.