i was having a play with my A100 and i noticed that when shooting in Raw+Jpg i only get 3 continuous shots before it has to write to the card where as with Raw only it manages 9.
Is there any real benefit to working with Raw+jpg?

actually what you are seeing is an embedded jpeg thumbrint.I shoot RAW + Jpeg but only as I thought I couldn't view RAW on camera.
Just tried it and I can view RAw on camera