I use a 70-200 f/2.8IS and it has 2 modes of IS (stationary and panning) and I can say that you really do need the panning IS for really getting good pics (along with 5fps + fast CF card).

The 70-300mm has the 3gen IS but I donno if it has the panning IS, if it does its worth it.
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extreme q vaporizer
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The girls next door advice