In Leopard the Dock has a new preference you can set so that when you start applications, they don't bounce up and down in the Dock while the application is starting. Instead of bouncing the colored dot next to the icon will pulse when the application is starting.

To set this go to the System Preferences and select "Dock". Then uncheck the box next to "Animate opening applications". Once you do this the icons in the dock will no longer bounce when applications are started.