http://www.blograndom.com/blog/2010/02/change-volume-key-step-size-in-ubuntu/
So, to change the effect the volume keys have:
Press Alt+F2 to bring up the “Run” box. Type in “gconf-editor” and press enter. Select “Apps > gnome_settings_daemon“ On the right hand side you’ll have a single option named “volume_step“ Change the numerical value (6 by default) to a lower one (3 seems pretty good)