Mkay, so I had my car on jackstands to do my brakes, and out of curiosity, put the car in gear and looked at the wheels spinning...the driver's side front wasn't spinning... So is that a function of the "wheels that slip to the wheels that grip" theory, or do I have an bad diff or something?
Could be a slip but it shouldn't be when the wheels are not touching anything. Have you try holding the other side wheel with something(or jack back down) and put into gear again? If you do that and the driver side front spins then I guess its a slip thing.
What year and model is this? If it's anything but an STI, you have an open front diff. One wheel spinning is normal.
Even a helical diff('05 up STi front) will spin one wheel without any torque to bias to the other side.
what these guys said. Open diff = wheel with least resistance spins. IE: if the drivers front was not spinning the caliper may have been dragging a touch more then the passenger side caliper or the wheel bearings may be tighter on the drivers side... Nothing to worry about.
I *think* it would take more than a little resistance to keep it completely stopped. the rotational inertia alone would transfer at least some power across an open diff. I wouldn't be alarmed.....but I would definitely go over that corner with a fine-toothed comb. especially checking the bearings. BUT, yea, since you just did the brakes. if you compressed the piston on one side more than the other.....maybe step on the brakes a few times to make sure things are pretty much even and try again.