I bought an extra long (350 mm, they didn't have 300 mm) seat post because the on that came with the bike was a little too short and I had too much bend in the knees. I tried it today and it work very good, makes all the difference. I feel like I'm sitting 10 feet in the air though and am going to hit my head on every branch on the trails.
I have been wearing shorts (not bicycle shorts) this summer while riding except for a couple of times. The two times I wore long pants the weight/pressure from the pant leg would make the left side of my left knee cap hurt enough that I had to stop riding. The first time was before I started stretching and strengthening and it started hurting quickly. The second was after I started stretching and strengtheningand it took quite a bit longer. Today I wore long pants because it was cool outside and with the new taller seatpost there was no pain. I noticed that there was almost no pressure on my knee from the pants because my leg was straighter. I took a padded, slip-on knee support with me and was going to wear it but I figured I would the seatpost a shot first. I am getting this bike, my knees and my riding technique dialed in.