I know subframe bushings are a common hot topic in the BMW community. I literally just had mine replaced yesterday and I can't say enough on how much of a difference it has made. For those of you who don't know I have a 2000 E39, and the subframe bushings had never been replaced before. I have just a hair over 81K miles at this time and the ride is so much better it is unbelievable.
Below are some pictures of one of the subframe bushings removed from my car. I took a saws all to it after the fact to show you what the center looks like. I thought it was pretty cool.
Top of the subframe bushing
You can see the metal inside the rubber in this pic. It's kind of scary to think that this part is responsible for holding the subframe onto the back of the car
As you can see in this pic, the bushing itself does not look too worn at all. When compared side by side to the new bushings it was almost impossible to see any real difference. This led me and my mechanic to believe that thee rubber and metal becomes fatigued after years of use but it doesn't necessarily look like that on the surface.
Honestly, the difference before and after is amazing. I was surprised and my mechanic was even more surprised. The rear end of my car had recently begun to feel like it was a little lose and I thought it was also kind of bouncy.
Now, the rear end feels solid as ever. The bounciness has been eliminated 100% and the lose feeling is no longer there either. This morning I took an entrace ramp onto a local highway about 10mph faster than I'm used to.
Now, I need to replace my front UCA's and LCA's and I'll be set for a long time to come. I highly recommend you get subframe bushings replaced if you're over 60K miles. It really does make a huge difference.