Short answer: There's no known way to actually speed up the animation.
But you might be able to make it marginally faster with a few tweaks.
Your best bet is to get one of the 3rd-party "tweaker" apps such as Cocktail or TinkerTool and disable any of the eye candy related to the Dock.
I'd recommend TinkerTool as it has more Dock-related options right now.
In particular, I'd recommend turning off "Use transparent Dock icons to show hidden applications". And turn on "Disable the three-dimensional glass effect of the Dock".
This will likely have only a minimal benefit, but it could help a bit.
And if anyone ever does figure out how to speed up that animation, it'll be the teams at Cocktail or TinkerTool, so having one of these apps means you'll probably be one of the first to know.
ETA: Fastest way of all: disable Auto-Hide.
I keep my Dock on the right side and it takes up very little screen real estate. It's mostly the vertical pixels that are precious.
And with Lion's new FullScreen feature, if I ever really need to hide it to minimize distractions, I just go FullScreen with the current app.