There is a slight wibble of the chest when someone punches and currently, some renders such as capes and amulets do not follow this behavior.

Some things DO though, like IE's Capacitor Backpack and Thaumic Perihpery's Pauldrons (even though Thaumic Periphery's quiver does not). Since this can be observed with Thaumcraft's amulets I figured it should be reported here.