Unified Switching between Keyboard Layouts in Various OSs
Yes, should be possible. You just need to unify your keyboard shortcuts in each OS. 

For OS X it's in "System Preferences" → "Keyboard"/"Keyboard Shortcuts" for Snowleopard it's in "Keyboard &amp; Text Input" on the left side and then you enter your desired shortcut by clicking on the assigned shortcut and pressing the combination you want.  

Note that cmd+space is usually assigned to Spotlight search, so you would need to change that too.  



And I think you know how to change it in Windows and Ubuntu, or you're able to find out - right ?