It should also be noted that when changing the engine mounts it is appropriate to replace the transmission mount as well if it has not been already.
I had moderate vibration from all three mounts, replaced the two engine mounts, and judging from the vibrations and shifting hesitation my rate of transmission mount wear has increased dramatically - my thought is that now that the engine is solid the transmission is getting more torque more quickly (it's not being soaked up by bad engine mounts) and further stressing my bad transmission mount.
don't be cheap, do all three at once.