I'm at 62k miles now with 30k+ of those miles on Eibach springs. I thought the ride was getting pretty harsh about 10k miles ago and thought maybe it was the shocks. I just replaced my tires and everything feels good again. I guess the rubber compound on the tires near the end of the tread life was much harder than the compound used for the rubber near the beginning of the treads.
09 E90 M3 - Interlagos Blue / Black Novillo / Sycamore Anthracite / Eibach / HRE