Ultra Edit (my favorite editor) is finally making a version that will run on Linux and Mac. I think that this is a very telling step. It may mean that software makers are finally feeling that Microsoft is losing it's grip on the OS.
Even without some of the more popular pieces of software being available for Mac, and to a smaller extent Linux, people have been switching away from Windows.
If Software Vendors update their applications to work on these other systems, I expect that even more people will be willing to make that leap.