Rubio will be very good, he might be great. He's still growing, he will add more muscle, and he's improving his shooting. Still very young. He will go to the NBA next year.
Ricky was a huge scorer when he needed to, competing against boys of his age, but he was very young (he hadn't turned 15 y.o. when he played his first ACB game) when he started playing at the pro level in Europe, so he was playing against bigger, stronger, more experienced players, and his coaches taught him to take advantage of his defense and BBIQ. When he developes his body, he'll be a totally different player, not Maravich, not Nash, but a very good player in the NBA.
He was 17 at the Olympic Games, he'll be just 21 when the 2011-2012 season starts (lockout or not), six months older than Rondo when he entered the league. You should compare Rubio to John Wall, or Evan Turner, not Rose or Rondo. Anyway, I'd rather have Rubio than Rose
right now... Rondo is (in my opinion) better than Rose and Rubio.
His season in the ACB has been solid, he rarely makes stupid plays like he did yesterday. At his age, he's very serious if you compare him to Sergio Rodriguez or Raul Lopez, the flashiest PGs in Spanish basketball.
I think he wasn't meant to play so mamy minutes yesterday, but Calderon got injured (again... he's very unlucky) and he will miss the World Champs. So Ricky will be the starter, and hopefully we will see Ricky vs Rajon in the semifinals.
Ricky Rubio and Rudy Fernandez played in DKV Joventut, the black and green team in the ACB, so they'd look great in Celtics green

It would be very nice