I've got a set of polybushes for my Disco 1, but haven't fitted any yet.
My daily car ia a VW Touran that I fitted a Golf R32 drivetrain to. My wife has a standard version.
I used PowerFlex on them: The entire front end on mine is polybushed and half the rear. Hers is mostly done in the front and also half the rear. Mine has a few fancier ones, for additional adjustment, as it's raised up about 25mm.
I have noticed a tiny amount addition harshness over really rough surfaces (tarseal surfaces breaking up and corrugations etc), and slightly higher noise on course chip seal, but the extra resposniveness is impressive and the additiona tyre life.
When I polybushed the wifes, she didn't even notice any difference, good or bad - HAhaha!
It is important to get decent stuff though.