Re: What I really don't understand...
> Is why do Mac users still pay for Parallels Desktop when VirtualBox is free?
Why buy cheese when chalk is free (dig it out of the ground) ?
Yes, at the basic level they do the same job, but they do it differently. Parallels has some features that, at a quick glance, VirtualBox does not.
For example ... To a certain extent (it's not perfect), Parallels can make your Windows programs appear very much like part of the Mac - ie instead of having a window with the virtual PC running in it, each Windows program has it's own windows intermingled with the Mac ones as if they were Mac programs.
I also note that VirtualBox has "experimental support for MacOS guests. Parallels 8 had full and supported support for MacOS guests* which was very useful for me when I upgraded my OS and had to keep a copy of my old system running for the handful of (old) applications that don't run on Mac OS 10.7 or later.
* Some caveats apply :(
Plus, when you've been using it for as long as some of us have (looooooong before VirtualBox and other upstarts were around) then there's a certain amount of inertia - it's a lot easier to upgrade than to start again with a different package. It's not that expensive either for what it is - the upgrade (they come every couple of years in general) has just cost me less that £40. So something like £20/yr or less - which isn't a lot of money (I can spend more than that on a single round of drinks). If it cost significantly more then I'd have seriously considered switching by now - but as it is, it's not worth the cash saving and I've more pressing demands on my time.
Sometimes "free" isn't the be all and end all. Parallels is "just a tool" for me - one of a long list which includes both free and paid for options. And it's one I've been using for around a decade - before that I used Connectix Virtual PC, until Microsoft bought it and stopped development of the Mac version.