We fitted the blue polybushes to our P38 about 6 years ago, just after we'd got it. They weren't cheap ones either, they were made by Polybush.
At the time, it tightened the car up and improved the ride significantly but after about 12 months the car started to feel like something was wrong. It started wandering on the road and didn't fill you with confidence when on narrow roads. I put it back in the air on the ramp and went over everything with a bar but wouldn't really find anything that looked that bad so we kept using it.
A few months later it started to develop a horrendous vibration if you hit a pot hole or an uneven road surface. It almost felt like the car was about to shake itself to pieces. The only thing you could do to stop it was to lift off and let is slow a few mph and then normal service would be resumed.
I put the car back on the ramp and got the long pry bar out and found movement in the front radius arms.
Water had gotten in between the polybush and the hole in the radius arm and corrosion had occurred so the bush didn't fit properly in the hole any longer. When trying to take the bolt out to remove the radius arm the metal insert in the middle of the polybush had corroded to the bolt as well. No amount of battering the bolt would make it shift and because the bush was there I couldn't get the oxy acetylene in to heat it. It took hours to clean the radius arms up to a point where they were fit to take the LR bushes.
In the end I had to use a very thin angle grinder cutting disc to cut the bolt out inside the mounting points on the axle to remove the bloody radius arm and replace all the bolts on both radius arms.
At this point I bought genuine Land Rover bushes (all of them) and my Dad made a tool on the lathe to fit them as the genuine bushes need compressing as you press them into the arm. When they come out of the tool they expand slightly so they're a very tight fit into the radius arm.
5.5 years later the genuine bushes are still tight, there's no wander or vibration from anything in the car and it drives spot on. The only bushes you couldn't get from LR at the time was the rear radius arm bushes so I had to fit aftermarket ones to them.
Personally, I'd never fit polybushes to anything ever again, the longevity of them I found awful and they're no cheaper then genuine. The only benefit is as mentioned above, they are very easy to fit as they come in two halves with a metal tube that pushes into the middle of the bush.
I'm sure others have probably had better results but these are my findings on my car using bushes I bought :)
1995 4.6 HSE - Biarritz Blue - Breaker
2002 4.6 Vogue SE - Alveston Red
2007 4.2 Supercharged - Java Black
2012 4.4 TDV8 Autobiography - Baltic Blue