Last time I tried that meant having to do a rather slow and disk hungry export followed by an import. Was I doing it wrong and is there no way to just copy the disk and machine definition, or are there other ways already?
I never do the export/import process for that exact reason.
If I need to move a VM for some reason, I copy the entire VM directory to the new location then open VirtualBox and use "Machine" -> "Add ..." and select the directory with the VM config and files.
I've not moved VM's between Windows and Linux, but it works fine going back and forth between OS X and Windows. The only caveat being that you have to re-visit the VM's settings for things like host volume mapping and especially networking config.
Last time I tried that meant having to do a rather slow and disk hungry export followed by an import. Was I doing it wrong and is there no way to just copy the disk and machine definition, or are there other ways already?