In Great Expectations, Pumblechook states that Pip's fortune is "well-deserved." This is a great change from how Pumblechook treated, and thought of, Pip when he was younger and only a blacksmith's apprentice.
Some may try and find the good in Pumblechook and state that he is being honest when he tells Pip that he deserves the wealth which has come his way. Pumblechook knows what a hard life Pip had when he was younger, especially at the hands of Mrs. Joe, Pip's sister. Pumblechook may actually think that Pip, after all he has been through, deserves the good fortune.
On the other hand, some may think that Pumblechook's true nature is simply to strong to be covered up by a lack-less and sarcastic statement regarding Pip's good fortune. Pumblechook is a snob. He only wishes to show off (as he does with the wine and the soldier's at the beginning of the novel). Once Pip gains his fortune, Pumblechook most likely believes that it would be in his best interest, financially, to be friends with Pip.
He is simply flattering Pip in the hope of getting something out of him now that he has money. Dickens is demonstrating the hypocrisy of many humans as well as the power of money. I am reminded of Mark Twain's novel The Prince and the Pauper and how people's attitudes towards the two boys changed after they changed places. Pumblechook had a low regard for Pip when he was mererly a blacksmith's apprentice. Pumblechook is a phoney.