Squeaky-ness and stiffness (imo) have to do with the throw-out bearing. I went in due to squeaks and the head tech said it looked like there was very little lubricant on the bearing. Many people have mentioned this in this thread. Busted firewall welds also contribute
The clutch assembly seems to be finicky and I think it just doesn't allow for sloppy driving. I also experienced pedal vibrations after a hard pull... but I don't get it anymore. A couple people hinted that mistiming clutch release and throttle position can cause this vibration.
The easiest first step is to take it into the dealer if you have a constant issue like squeaking. For the vibration issue, I think its mostly in shifting technique. A lot of us new-gen wrx owners are first time wrx drivers so perhaps it takes time to get used to shifting properly. I honestly don't get any of the vibrations in the clutch pedal anymore.