O.k. this is going to sound like I'm an idiot. I almost didn't reply, but I thought this might be a slight chance in h#ll for some clutch shudder problems out there.
I had the clutch shudder on my 00' coupe. Brought it to the dealer (who I really trust, their service manager is great). They let it sit overnight (cold outside) and felt the shudder too. THey had the car 5 days (gave me a loaner) because they didn't feel it was actually a clutch problem. After a half dozen calls to the Subaru tech line they decided to replace one of the o2 sensors. Guess what? it worked. No more shudder.
I know this doesn't make sense, but I thought it might be a possible solution to those who've had their clutch replaced only to have the new clutch do the same thing.
It's worth a shot...
If anyone's interested I'll see if I can scrounge up the part # for the part they replaced (just email me)