I personally agree with the demotion of Pluto, but that is my opinion. So that leaves us with 8. As Les said, I doubt we will find any other objects in the future that will fit the bill for inclusion as a planet as they would be so far away they would be unlikely to be in a "planetary" orbit. As for the number of "Plutinos", I would guess this will grow to be much larger than the number of "planets", perhaps dozens...it is just a pity Pluto won't be the biggest

Mickey would turn in his grave