I’ve just got my new road bike frame with and internal headset with carbon races and a full carbon BB30 bottom bracket, should or shouldn’t I use grease?

None of the moving parts will be carbon.

I’d put carbon assembly paste on all the parts which contact the carbon.

Carbon assembly paste on bearings touching the carbon?

Yep.

why in gods name would you put carbon paste the bearing seats in the headtube?

don’t put paste in your headtube, this is only likely to mean the bearing doesn’t sit true in the cup if you have even slightly more on one side to the other.

carbon prep paste only need be in the seat tube.

Using a low strength retainer for bearings might be a better idea eh?

Loctite do an entire range of products which do exactly what it says they do

http://www.boeing.com/commercial/aeromagazine/aero_07/corrosn.html

“Fiber-reinforced plastics are corrosion resistant, but plastics reinforced with carbon fibers can induce galvanic corrosion in attached aluminum structure.”

“For example, graphite fibers, which are used to reinforce some plastic structure, present a particularly challenging galvanic corrosion combination. The fibers are good electrical conductors and they produce a large galvanic potential with the aluminum alloys used in airplane structure. The only practical, effective method of preventing corrosion is to keep moisture from simultaneously contacting aluminum structure and carbon fibers by finishing, sealing, using durable isolating materials such as fiberglass, and providing drainage. ”