Am I the only one that loves the push/pull zoom?
I find it great for football (american, but both would probably apply; as well as any other large field games, rugby, polo, baseball, etc.), you can see nearly the whole field at 100mm to scan for interesting action, and almost instantly be at 400mm to get in to the action. If you're constantly going from one end of the range to the other, it's much faster with the push/pull.
The push/pull was much less useful, but in no way a hindrance, for things where I was staying at the same focal length for long periods of time; like when I shot a "Dirty Girl" mud run.
Would I want all zooms to be like that? Absolutely not! But I do think the 100-400 and it's common uses lend themselves to the more expedient, brute force method, that the push/pull provides.