As far as cleaning suggestions, I've used carb cleaner and a dremel with a nylon brush wheel on pistons. Works pretty well, just make sure to keep the deposits wet with cleaner. I started a thread on it a while back. Gasoline and detergent soaking solutions were also suggested.
However, unless you have a real problem from carbon buildup, such as pinging from increased compression or detonation from glowing carbon deposits, you'll probably notice no change in performance. I'd save the cleaning for when you have head work to do. If you're just doing a base gasket or pushrod seals I wouldn't bother unless you're jonesin to spend a few hours gettin dirty.
