We've not found a good Mobi converter/creator for the Mac, so all of ours (I work for a publishing company) are being done under Windows. However, they're still being done on a Mac, as we run Parallels and then run Mobi Creator under Parallels. (Same would work under VMWare's virtual machine.) If all you need it for is ebook creation, though, that's a pricy solution, by the time you buy Parallels and a Windows license.

Oh, and Happy Birthday!