I took JRL's advice and replaced all my engine mounts with new Volvo-stock ones. It took all of 3 hours including a trip to Sears for a long 1/2" extension.
With the old mounts, not only the steering wheel vibrated on neutral, but I could feel it through the seat. The whole car was groaning in low speed acceleration and coasting. With the new mounts it's as good as any new S60 I have driven. It's not Honda-smooth, but it's 5-pot Volvo smooth
The main engine mounts looked okay but they were sagging a bit. Now the engine sits 1/8" higher.
The car has only 58k miles, but the engine's been sitting on the mounts for 8 years...
With the old mounts, not only the steering wheel vibrated on neutral, but I could feel it through the seat. The whole car was groaning in low speed acceleration and coasting. With the new mounts it's as good as any new S60 I have driven. It's not Honda-smooth, but it's 5-pot Volvo smooth

The main engine mounts looked okay but they were sagging a bit. Now the engine sits 1/8" higher.
The car has only 58k miles, but the engine's been sitting on the mounts for 8 years...