To space save or not to space save. Personally I have a full sized rim as my spare, but in all my 13 years of driving I have only ever had to use my spare once.
We used a space saver on a VE SV6 Commodore during one of our test trips before it was released and the Chassis engineer who did the dynamics and handling for the car said they basically pose no real risk if you bare in mind that it IS a different rim to the other 3x on the car.