In guitar amps I think particle board (actually it's MDF - "Medium Density Fiberboard") is used for cost savings. I think the worst thing about its use is the extra weight it adds. Clearly it kills cabinet resonance - and that's not a desirable thing for a guitar cabinet. This damping characteristic (and weight) make it the preferred material for Hi-End "cost no object"
audio speaker cabinets though. It's used in constructions of audio speakers that cost tens of thousands of $ a pair - and the manufacturers brag about it. They put a nice hardwood veneer and finish on it and it looks fantastic.