I'm having an issue very similar to this. The clutch seems normal for the first half inch or so until it begins to engage, at this point it becomes gritty and has a vibration in the actual pedal. If you continue to push it all the way in the grittiness and vibration go away, but come back when it reaches the same point while letting it out. This happens when first starting the car, not after it reaches a certain rpm like others have stated. The clutch continues to do this for awhile, at different times it goes away but always seems to come right back. I don't launch the car or drive it very hard at all other than a few spirited pulls here and there. I also feel as this will be one of those problems that the dealership will say its a non-issue or claim they can't reproduce it :/
2011 WRX 20k miles, vibration has been happening for atleast the last 7k miles.