Well this seemed like it was a lot of fun!
I think you did a fine job, but here are somethings I would like to point out.
-Remember to anticipate the shot before it's going to happen. If you can find out what trick he or she is about to do, then you can position yourself a little better.
-I'm sure you did this, but remember to always shoot as many frames as possible. Set your camera into continuous high, and just shoot as fast as your camera can. With this, you can create a short 'montage' of a trick, or a grind, and make a 8x10 or something and have it all the frames laid on out on it.
-It's good and a great action shot. But, there is too much in the frame, and it's a bit hard to see how he ollied up. Maybe if you moved a bit more to your right, (or the other side), and made a bit tighter crop...? But overall it's fine.
-Okay with this one, it kind-of lacks a 3D perspective. It's a bit too straight-forward. This is kind of what I meant with the above photo as well. Maybe you could try a different perspective/angle so that more of the subject can be seen, in more of a 3D view.
-Looks like you were in the right position. Just that your shutter wasn't as fast as your subject. But that's fine, it adds a sense of movement. This might have looked cool if you were on the other side of the rail as well. But again, good job.
-Good eye for a photograph. I like different compositions like this, so in my opinion, it's 'cool'.
So overall, I think you did great. I think you should try and go there more often. I'm sure more skaters are going to be asking you to take pictures of them.