WINE development has come quite far in recent times for being able to execute windows binary files in Linux; so much in fact that I'd be willing to bet that your everyday items you use could likely be run fairly easy now adays...
FireFox ad Thunderbird both run in Linux just fine, in fact, they dev there first before making the Windows port. Same with Pidgin.
MacOSX in fact is a BSD varient, which can run Linux code (when set properly), and now that they have x86 processors you can also run Windows on them as well.
Myself, I'm not a Mac fanboy; though I had to use a dualboot MacOSX/MacOS9 machine when I Was at Adobe for tech queries.