I probably won't be getting Leopard for a few days to a few weeks but when I do one of the things I wasn't looking forward to was the new dock.
I've tried it and I hate and despise every pixel of it. No need to rehash the arguments and if you like it, well... more power to you. But I'm overjoyed to find an item on Daring Filreball showing you how to get rid of the reflective, glassy, 3D horror:
defaults write com.apple.dock no-gass -boolean YES killall Dock
This turns the dock into something of a hybrid of the Tiger and Leopard docks. It loses the rubbish 3D effects and turns it into a kind of smoky glass translucent Tiger dock. The net effect is that it looks less hideous and the the running lights actually have enough contrast to show up.
All in all I'd say it's a huge improvement.
Update: Aha, reading a later item I see that the shipping Leopard already ditches the crappy 3D effects on the Dock when it's placed on the side of the screen (which I always do anyway).