I'm starting to think they have some defective throw-out bearings. Mine has been slightly audible (ticking) from day one and seems to have good/bad days, but has only gotten louder over time (still pretty minor with no squeaks, just light ticking that goes away when you disengage the clutch). I noticed the vibration near the engagement point around October or so and it has been coming and going since then (often worse in the cold, but not always and it can do it when I leave for work and have stopped before I'm halfway there). No signs of slip thus far and I'm now at about 15k miles. The vibration is disconcerting, however.
I've read in different threads on here lack of grease on the clutch fork and now a loose bearing. Add to this all the threads about odd premature clutch failures on recent year models, I no longer have much confidence in Subaru's clutches. I do know my clutch was VERY light when I first got the car and steadily got heavier as time went on (dealer even remarked this would happen when I mentioned how light it felt compared to my '04 WRX that I traded in for the '11). My last WRX ('04) I got used at 2 years, 36k but it felt pretty even throughout the time I had it (traded at 80k miles).