I heard one guy did a custom install on one of these using the 4g drive for / and the basic essentials, the 16G card for general system stuff (/usr/ /bin etc.) and a 32G usb stick for /home
His rationale was that he could just take the usb stick around to keep his files secure (doesn't matter about the system stuff) and also use it to do any file copying.
On the one I use for work I've thought of putting the whole of the system on the 16G drive, and using the 4G one for /home. This is because I run quite a lot of applications, but don't store much data on it.
Don't you just love a system that lets you organise things the way
you want to