I have an 01 AWD RX300 that acts as you describe if I'm in the wet especially. Mechanic explained to me that the "automatic brake force distribution" system will sometimes "hunt" causing the same affect as ABS at the brake pedal but much lighter.

 

I think LastV8 may have hit on it. If the wheels were removed for a pad inspection etc. and then replaced and retorqued with to much force this could have warped the rotors (the infamous "revenge of the impact"). Mentioned in this months Popular Mechanics.
Let us know what you find out.
Jim

 

Tires will absolutely flat spot if left sitting for long periods. Driving at a speed of 100mph for a short time seems to correct this. I work at the Porsche dealer. I suggest you complain a bit more about the brakes. Its good to be nice, but sometimes its the squeaky wheel that gets the oil.
Good Luck!

 

On the wheel torquing issue, some recommend torquing the lugs in stages. Example, 50n/m, 90n/m, 130n/m. Just a thought.