Certain applications have a very annoying (to me) feature -- they bounce their Dock icons. I keep my Dock hidden, mainly because I don't use it all that much, and I find the bouncing icons quite annoying. Some programs allow you to control Dock bouncing via their preferences (iChat comes to mind), but for others, control of the bouncing is out of the users' hands.

Thanks to a simple Terminal command, however, you can permanently prevent Dock bouncing by any application. In Terminal, enter these two commands:

$ defaults write com.apple.dock no-bouncing -bool TRUE
$ killall Dock

When the Dock restarts, you won't see any icon bouncing again, ever. An ideal solution would be a per-application setting, because there may be apps for which you want a bouncing Dock icon. Lacking that, though, I'll take the no bouncing solution. To reverse this, just repeat the command, replacing TRUE with FALSE, and then kill the Dock again.

For an easier method of implementing this feature, see this hint.