What is confusing me is the good vs bad of polyurethane.

Polyurethane is bad for control arm bushings (unless you're a street racer) because the stock rubber mounts absorb more of the constant off-road shock. That's kind of the feel I get from many threads.

Polyurethane is good for replacing body mounts when you do a bodylift because it helps minimize sway and vibrations.

Polyurethane is bad for anti-sway bar bushings because it resists movement more than rubber, making your truck flex less offroad.

I used some polyurethane on my OME shocks when I installed them and as a result, I can sometimes hear squeaks coming from the back of the 4runner, particularly on rough roads. Will there be more squeaks from the poly body mounts if I replace them?

 

Poly will squeak more than rubber but if you lube them up good with silicone grease (I use dielectric grease mixed with graphite powder) they are fairly quite.

I have poly upper control arm bushings and poly sway bar bushings and poly leaf spring bushings with no squeaks.

 

Poly only squeaks when there is motion between the part inside the bushing and the bushing itself. If poly body mounts squeak, that means there is something moving (like the body) and that is not good. With the body mount bolts properly tightened, there should be no squeaks. I've run poly bushing for about 9 years now and never had a single squeak:
- http://www.4crawler.com/4x4/CheapTri...shtml#Bushings

Poly is stiffer than rubber and flexes less. Keep the poly greased (I use graphite loaded wheel bearing grease on mine) and it won't squeak. I find it also last longer, I have had a set of rubber spring eye bushings disintegrate in one wheeling trip. Poly bushings last me many years and they seem to flex just fine: