I have a couple of Powerflex bushes on the back end of the front wishbones on my Alfa. The originals are voided rubber, but the early 164 suffered from dreadful torque steer on poor surfaces and these make it noticeably better. However, they don't have the same compliance as the originals and I pay for that in a slight increase in harshness. The car doesn't feel quite as refined. They seem to last about 30,000 miles before you get any noticeable wear though.
I absolutely refuse to have them in the rear suspension, which is a multi-link setup. There's a big rubber bush (also voided) in the leading end of the trailing link, attached to a bracket on the bottom of the floorpan. As the suspension moves up and down, this moves in a conflicting arc with the rest of the suspension arms on the back - effectively, pulling each rear wheel forwards slightly as it rises over a bump. The original equipment void bush, allows the link to change length slightly to avoid this. The polyurethane ones don't. This puts a bigger load into the bottom of the floorpan and I worry about increased corrosion as it flexes.
There's also an engine stabiliser bar that has one small bush (engine end) and one big bush (bulkhead end) in it. I tried a PU replacement in the big end and very quickly took it out - it was trully horrible! Felt like I'd taken a V6 engine out and replaced it with an old Perkins diesel!
In short, I would consider using them in applications where they only have to rotate, rather than change shape.
