This post asked the question: who is the most under-rated player on the 49ers, with the corollary, who is likely to step-up and have a unexpectedly productive season next year.
My choice is a defensive player. Before I name him I would like to acknowledge a number of players who have played extremely well on defense. Of course it starts with Willis. This is Patrick Willis' team, in my opinion. He defines the 49ers. In addition to Willis, Haralson and Brooks, as well as Lawson and Spikes have played well, particularly late in the year. In the secondary, Goldson has stepped-up as a play-making safety and Spencer has played quite well at corner. On the front, Justin Smith is an amazing 3-down player; Franklin and Sopoaga have been good against the run. Franklin's play in particular has helped the line-backers tremendously.
My suggestion for under-rated player in Ray MacDonald. From the championship Florida Gators, he was the 3rd round pick in 2007 (after Willis and Staley). I invite others to look at the film and critique this choice and propose others if you like. To focus the argument, I ask this question: how were the 49ers able to put so much pressure on Warner in their 2nd game against Arizona. I think that, in addition to the better known and more lauded players, McDonald ( generally at left tackle on passing downs (and there were quite a few passing downs)) played a major role in facilitating that pressure. That pressure, an impressive team effort, was critical in stopping a potentially potent and dangerous offense.