To add my two cents, I have a fairly good impression on this Russian rookie.
While his late uprise in the Chinese GP was mostly down to tyres, Kubica didn't make any progress and was in the same car. It works in his favour that he can manage to save the tyres for when they are most useful, and I'm confident he is well supported within Renault. That team does not want to make mistakes made with Piquet where Briatore favoured just one driver.
There is still some work though, he spun during the race in China too, allowing two cars to pass him. We'll see how he does in dry conditions with some race experience in the bag.