Pete,
This formation has 3 in the back,typically flat, with 5 packed in the midfield, and 2 up top. The outside mid-fielders (Donovan and Lewis) have a great deal of running to do in this alignment. This is a popular formation and allows for sufficient strength in the mid-field area and those players can provide defensive numbers as well as transitioning into the offensive end quickly. Many colleges and even my former high school/club program used to use this formation depending on who we were playing.
Warren