I got a nail in one of my rear tires about 6 months ago. I replaced the rears with PSS and kept the front PS2 (which are fairly new). I've had absolutely no adverse reactions from the car. I agree with the opinions set forth in that you may experience a little extra understeer at the limit.
I simply can't make myself throw away 2 perfect good, expensive front tires either.
I actually mis-titled this thread it should have been "Running PSS Front/PS2 Rear". I am assuming that with this setup the car would be more prone to oversteer since the PSS's will have more grip in the front.