Either I've been lucky or not used the car enough, but I have the EBC Turbogroove discs and Greenstuff pads on the front and they are fine; much better than the standard brakes.
I do notice them biting into the discs when really braking hard, not a judder but ever so slight vibration, almost like humming :eek13:
The other thing that you will notice is noise from the grooved discs - that's my only gripe. It's a constant fluttering noise from the pads going over the grooves.
If I were honest though, I don't know if the sort of driving I do warrants the grooved discs. When they're worn, I'll probably go back to standard discs with uprated pads - Mintex Extreme seem to be recommended a fair bit.
Hope that's of help.
Nick