I agree C Rogers took a step back, but Cully and Brown are very solid cornerbacks. Towards the end of the season and the playoffs the pass rush was non-existent so that didn't help. I honestly feel like Whitner, Goldson and Rogers were the weakest links in the secondary. Both safeties made a ton of mistakes in the playoffs. Cully got beat in the playoffs, but a lot of it was Boldin making plays and Whitner/Goldson making the wrong read/bad communication on some plays and putting themselves in the wrong place.
IMO the secondary wasn't the biggest issue during the season. We didn't have trouble with pass happy teams, but it was the physical, grinding teams like the Seahawks, Rams, etc that gave us problems. I am sure the Niners will draft depth at both the line and the secondary tho.