didn't see anything for nc here so I thought I would add some. I've only rode at 2 of the parks here so far. first is uwharrie national forest. cost is $5 for a one day pass. its roughly 16 miles of trails with easy to difficult. the most difficult is named "daniel" and it is rough! you'd better have good brakes on it. the rest of the trails are decent. the area is rocky, extremely on some and both you and your ride will take a beating. its been dry so its also very dusty.
second is brown mountain. my first time there was yesterday. cost is $5 also for a one day pass. according to the park map there is roughly 30 miles of trails, easy to difficult. unfortunately I can't give a good assement of the place as I was only able to ride on 2 of the trails (11 miles though). my uncles trailblazer gave up on him and I had to tow him out. from what I did ride there, it was some very good trails. imo, a lot better than uwharrie. although uwharrie is a lot closer to me. I will be going back to brown mountain and can give a better assesment.
if anyone else knows of some more here in nc, please post them up. I will update my info regularly.