Just ran some Subaru Upper Engine Cleaner on it - recommend two people for this job as after the engine kicks over you'll have trouble getting to the engine bay before the engine stalls.
Can't say I notice much of a difference which is surprising - my piston crowns were all carboned up last time I checked. Not sure if it's a placebo effect or not but I think the throttle response is improved a little bit.
One thing I did find out though is that my PCV valve is very oily - wonder if I should get a catch can
