I guess it beats all the cutting (and getting cut) with shielding tape, but I was never happy with the StewMac graphite product. There is the messy blackness aspect of it (as others have mentioned) as well as the relatively poor conductance (typically around 100 ohms from one point in a cavity to another). I visited Ken Lawrence's shop and he turned me on to CuproCote, which is a copper-based shielding paint (http://www.lessemf.com/paint.html
). It is a fairly thick water-based product that can be brushed on, or diluted and sprayed. I find that two coats works great, with very high conductance (2 ohms between points a few inches apart). It sticks better to bare wood than to painted surfaces, so a primer or at least good sanding might be needed for the latter. A 4 oz. can is about $30 - I have just finished two basses with big electronics and pickup cavities and used about 1/2 a can.