Had my intake off at 80K to fit new injectors and the carbon build up wasn't as bad as I was expecting, so left it. Think I'll wait until 100K before tackling that one!
As for Terraclean, unless they come up with a super aggressive detergent that can be injected into the intake, there's no point using their service. No one has yet come up with a quick fix of that kind. It's either walnut shell blasting or scrubbing with brake/clutch cleaner!