The ReadMe file in PDF format that comes with the migration program officially called the "Family Tree Maker for Mac 2, File Migration Utility Guide" gives this overview:
The Family Tree Maker File Migration Utility converts Family Tree Maker Windows files so they can be opened on a Mac (and vice versa). Because Family Tree Maker 2012 and Family Tree Maker for Mac 2 differ significantly from previous versions of the software, you can’t migrate older files directly into the new versions. For example, you can migrate a 2012 Windows file to a Mac 2 file, but you cannot migrate a 2011 Windows file to a Mac 2 file. If you wanted to use a 2011 Windows file in Mac 2, you’ll need to migrate the 2011 file to a Mac 1 file and then import the file into Mac 2.OK, so you have to be awfully careful about which versions of which programs you have and want to migrate. But the Utility Guide does say, "Files created in older versions of Family Tree Maker versions 5 to 16 (.ftw and .fbk files) do not need to be converted using this tool; they can be imported directly into Family Tree Maker for Mac 2." I had no trouble migrating my Family Tree Maker file from the first Mac version over into the newer Mac 2 version.
As with most file conversion processes (or migration or whatever) you have to be careful about where the files end up on your computer. Fortunately, all of the files for Family Tree Maker are stored in the Family Tree Maker file created when you install the program. This is not my first choice of where to store my data files but it does simplify the problem of locating the latest version of the files that you have on your computer.
I commonly find people with several different data files, all created at different times, on their computer. I get around this problem by including the date the file is created in the file name.
One really strange limitation of the new Family Tree Maker files is that even though the programs will synchronize with an online Family Tree on Ancestry.com, each program has to have its own version of the Family Tree online. So, for example, if I have FTM 2012 on my PC (or my PC partition on my iMac) then I can synchronize with an online Family Tree, but I cannot use the same online Family Tree to synchronize with my Mac version (on the same computer). So there is no way to keep both my Mac version and PC version in sync. In addition, you cannot use the program to sync information between computers, you can only create a link with a Family Tree on one computer at a time. If Ancestry.com overcame that one significant step in the process, that is, letting the users sync to more than one program, you could really have a hugely valuable way to collaborate. For example, if this were true, I could do all my research on my Mac 2 program and then sync the data with my online Family Tree File. Then my daughter, living across the country, could sync her FTM 2012 PC or Mac 2 or whatever to the same Family Tree. But, Ancestry.com hasn't gotten there yet.