i cant really see how too much?! although the drive shfts are connected the cv joints should compensate for any engine movement. get 'em done a.s.a.p though as driving round with knackered mounts can lead to all sorts of other problems. like, hoses being stretched/pulled all over the place, exhaust being moved in ways it never wants to.
this'll freak you out: get someone in the drivers seat and get them to try to pull away with the handbreak on, just see how far your engine will try to climb out the engine bay! freaky stuff!
also new engine mounts transfer the power alot better and you'll get a smoother ride!