That's the same thing that happened to my car a while back, and it's been happening again lately. The first time was about 8 months ago. The dealership did the usual "give it to us and we'll see if we can make it happen" kind of thing. I ended up getting a new flywheel, pressure plate, and clutch disk all under warranty. But I don't think that was the real problem. I thought that air in the clutch hydraulic system made sense, but what do I know? It seems to happen the most on cool, humid mornings. I have to pump the pedal about 8 to 10 times to get it back to normal, then it's fine the rest of the day.
Does anyone know the proper way to bleed the clutch? I don't feel like playing with the Subaru goofballs again.