Mazda Repair: hard brakes, booster unit, mazda mpv

Question
It is a 2000 Mazda MPV with about 99,000 miles.  I also just had the rotors machined about a month ago.

-------------------------------------------
The text above is a follow-up to ...

-----Question-----
Just about a week ago, ever since the temp really dropped down to freezing, my brakes aren't working properly when I first start driving.  They feel very hard and the car isn't braking.  Within about thirty seconds or a few hundred feet, all of a sudden they work fine again.  I've owned the MPV for about four years now and have never encountered this problem before.
-----Answer-----
yr, mileage?

Answer
there could be a few different reasons for this, first thing i would inspect is the pads,  are they some cheapo pads? I've had many problems with aftermarket pads.. 2nd i would see if there's a temporary engine vacume leak, (does the engine run funny when cold?) seen alot of intake gaskets leaking then they seal up some due to heat exspansion. 3rd  is to inspect booster unit and hose