I had this done about 4 weeks ago. It totally transformed the car ! The handling is better now than it was when I bought the car 1 year ago.
Ben Fricker damper Tech at silverstone serviced the dampers, I was without a car for 4 days thats all.
Cost me approx £450, but I had some internals replaced as they were damaged and I had new dials fitted. They were both put on a dyno too, to make sure they were equally matched. Excellent service !
A few people have had the shocks rebuilt at BG Motorsport if i remember correctly, a quick search and you should be able to find the thread with details of what they do and their contact info.