How easily does the program move between platforms (Mac and Windows)?

Very. The study files and all source file formats are fully transferable between platforms.

Keep in mind that file types on windows are determined by the three-letter extension to the file name. So if you create your study o a Mac, for it to be recognized as a HyperRESEARCH document on Windows you'll need to make sure the file name ends with ".hs2" (e.g., "MyStudy.hs2"). The same applied so source files as well ("MyInterview.txt", "InterviewAudio.mp3", etc).