I myself have three systems for working with sound, a MacBook Pro/Mbox for mobile recording and editing, a Windows 7/Digi002 LE workstation at home for smaller, more personal projects and access to a Mac Pro HD suite for larger projects. I find that I lose a significant amount of time and productivity moving between workstations.
If you're in a similar situation, what kinds of tools (software or otherwise) are you using to bridge the gap between Mac OS, Windows and/or Linux, as well as between multiple rigs?