I didn't really mean to start a new thread on this - it was supposed to be part of the "instability" one, but hey, we're going now.
I had similar experiences in the wet as you guys - very scary.
Then something about the wear pattern made my 100GS very wobbly at low speed - they wore into a sort of scalloped shape, which created a central ridge around the tyre -ok I can't describe it and I don't have a photo, but it was very weird. The bike would teeter from one side to the next. Made me look like a complete arse!
I never had a similar problem with Conti TKCs or MT 21s or Tourances. Ironically I felt much more in control riding on Knobbies than on the T66s.
I'm off GS's at the mo. Are Tournace's still the tyre of choice?