Your friend can log anything he wants....he can log SIC hours in a Cessna, he can log how many cars he sees while flying SIC in the Cessna, but when it comes time to get his license, he can't use that time towards his license.
What he can use towards his license is the experience he gains while flying with you. Even though he can't use it to lower hour requirements for a license, he can use it to make his training easier (and as a result, cheaper). When it comes time to start training, he'll have an advantage over someone who has never seen or touched an airplane. One thing he'll have to remember, is that he's still a student. Even with 200 unlogged hours, he still has A LOT to learn, and he should go into training with an open mind......
edit: oh ya...even though he's not licensed, it doesn't mean he can't use the radios or fly. Just remember that YOU are the PIC and responsible for everything he does. Don't go outside of your comfort zone when you let him do things and if there's any question about it, make sure that he knows that you're going to take over complete control of the airplane...