I've had two bad, long term experiences with shin splints, both brought on by running on hard surfaces and (I believe) an overlength stride resulting in heavy heel striking.
I agree with Ady in that the pain eminates from the centre of the shin. To me it felt like the front of my shin was being pushed against a round metal bar such as an iron ladder rung. At first it felt like just bruising, but built up week by week until each step was making my eyes water.
I had minor problems on and off for years until I changed my running style and haven't suffered since (fingers crossed).
In all cases though the pain was purely concentrated on the centre to lower half of the shin and to be honest I didn't have any trouble with the knee at all.
Hope it clears up soon.
Ian.