Is there any way to tell if the host that a script is running on is a VirtualBox guest VM? Ideally I'm looking for a cross-platform way. I would think this is next to impossible unless, maybe, something in the Guest Additions provides this.
Did some poking around and under Linux,
And the Windows equivalent (thanks to Andrew Koester for the pointer)
There is a Solaris equivalent, but I can't test it because I only have access to Sparc machines. But, for completeness, here it is:
In Windows, you can query for the BIOS information with WMI. http://msdn.microsoft.com/en-us/library/aa394077%28VS.85%29.aspx
I don't believe you're going to find a cross-platform solution, at least without going all the way down and reading it directly out of low-level memory. (In this case, you might be interested in the source code to dmidecode)