Everyone's perception will be a little different depending on personal tolerances, etc... but here's mine.
So far, I have put ~3000 miles with the springs on the car, including an ~800 mile trip up to NorCal.
Compared to stock, the car is a little harsher on rough roads, no doubt. I find that the car actually rides smoother with the edc set to normal or sport vs. comfort. In fact, contrary to what you would think, I've found that comfort should actually be avoided to promote a smoother
ride with these springs.
I have noticed no degradation in the rebound or dampening response to the shocks overall, as others have reported ala the M5/M6 boards. Perhaps more time and miles will tell.
Travel over smooth, well maintained roadways is superb and quite a fun experience with the tighter handling. This is purely a weekend car for me with maybe 3-4 track days per year, the springs, for me, make sense and I enjoy them. For others, perhaps those who use it as a DD or commute over horribly maintained roads, or who aren't too careful, it may not be the best choice.
Improved turn-in response
The car remains flatter on banking turns
less rake on acceleration
less dive on braking
can be uncomfortable on rough roads
An S.A. or S.M. who also happens to be a good friend or neighbor wouldn't hurt.