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This one's pretty obvious, but crucial, particularly for large businesses. Glenn Jones, an IT project leader who is heading up a Windows 7 migration for 11,000 users for a global corporation, explains that simply using Windows XP Mode to shoehorn old applications into Windows 7 would have created more complications than it was worth. So, Jones and team used the Microsoft Application Compatibility Toolkit to analyze more than 16,000 lines of data, representing 650 applications.

"We went through every single application that was on that list to identify if they were valid and still being used," Jones says. "The tool also helped identify some of them that were Windows 7-compatible."

After a lengthy analysis period, Jones and his company's team decided to eliminate many applications, while adding others, eventually settling on 341 applications that would be used with Windows 7. "We found a lot of opportunities to consolidate onto fewer applications," Jones says. "We had a few that still required Internet Explorer 7 but we were able to either give access to them through terminal servers temporarily, or upgrade them to become compatible."

Jones gathered key people at his company together for a four-week session on migration issues, including what the Windows 7 image would contain. But it turned out application compatibility was the most complicated portion. Looking back, Jones says he could have stretched out the whole migration analysis process to at least three months, and spent four weeks alone just on application issues.