So you can get sharp shots at 1/15 but you can you, with ver I of 70-200mm f2.8 at 1/30. The IS is not that bad as some folks made it out to be. It is the same IS which is on bigger boys like 300/400mm f2.8 IS or the 500/600mm f4 IS.
The IS was top-of-the-line in the 2.8 Mark 1 when it was introduced. Nothing against it and it certainly is impressive. But, as with most things electronic, improvements have been made. (That's why they came out with a 2.8 II and a 400 f2.8 II, etc.) The f4IS just happened to come out as an improved model first. Canon seems to be going through and refreshing lenses across the line. If I needed to freeze action in low light, I'd sure go for the 2.8 IS (either version 1 or 2). But, since I don't need that capability regularly and since I love the lighter weight of the f4, that's what I went with. Of course, no one mentions that the 2.8 version also provides a bit better focusing, at least on non- 1D cameras as the 2.8 is needed to use the cross type center point (I think).
