I've consistently said that he has already proven to have NBA level rebounding and outside shooting skills. He also keeps the offense moving side to side from the top of the key, which is a key ability for big men in the modern NBA.
He's still struggling to find a rhythm scoring in other ways. Whether that is due to length (getting his shot blocked) or due to inability, I think remains to be seen.
His defense has not been great. He is consistently out of position, he cannot switch onto smaller players, and he is foul-prone.
I'm still convinced that Yabu could score 16-20 points per game on a bottom-dweller team that needed scoring. The question is whether or not he can contribute to winning.
In other words, right now, he is more Mo Speights than Kyle O'Quinn. Both are productive players, but only one has contributed to wins in his career.
I don't see a reason why we wouldn't pick up his option. His teammates seem to like him. He has decent upside as an offensive-minded big. He is on a cost-controlled contract. I don't think his contract will have significant tax implications. Now, picking up his 4th year option might be a different question, as his fourth year will cost closer to 5 million.