While testing the glass effect on the MacOS Dock on Leopard, I was suprised to see a curious parameter in com.apple.dock.plist. It is related to the large size of the dock icons when magnification is enabled. The preferences pane let you set this value to 128 at most, but you can put arbitrary value in the plist file.

defaults write com.apple.dock largesize -int 256
killall Dock

And your dock will show bigger icons. To revert to a normal size, open the Dock Preferences Pane.