I have had mine on for at least 50k and yeah, the ST200's are going soft. Most of the firmness while driving is gone and there is a good bit of movement when braking and acceleration.
The only real problem I had with the ST200's was fade. If you drove really hard, for a short time, they would almost go limp. This was even after having them on for a week or so. But as for normal everyday driving, and I did a lot of that, they held up just like new for around 30-35K. After that, you could tell that something was missing. Noone else could tell, but I did.
Hope that helps.

Here is a picture of mine that I took a few months ago. I guess the suspension set-up had been on there for a little over a year.