This is a very good article on midfoot running, provided by the NY Times. It is the running form I have used for the past two years and I believe is responsible for me increasing miles into the ultra category without any injuries. It is an extremely efficient way to run.
The Once and Future Way to Run
By CHRISTOPHER McDOUGALL
Rediscovering the simple act of putting one foot in front of the other.
Happy trails my friends.