OG put up a clinic on the use of buybacks. While other teams seemed to be more reluctant to use them, OG will just chain them in order to win the battle at hand, vs planning for the future. It worked out for them really well.
I do have to say that one of dota's nicest play is to see sumail's storm spirit die on an epic battle, to be bought back and then instant warps(ball lighting) across the map and kill every one when all hope is lost.