Comment 39 for bug 527267

I played around a bit with some theme settings. Ted is actually right as the indicator-application uses a theme setting to generate the spacing around the icons. If you put or change the following line in the default style in your theme's gtkrc the gap between the icons in the panel should disappear (make sure that it is nor overwritten by another style later):

GtkMenuItem::horizontal-padding = 0

However, this setting also affects the menu which looks quite ugly afterwards (no spacing between menu items). To avoid this you can put the following line in the style which is assigned to GtkMenuItem:

xthickness = 5

I think this value should be increased by the same amount as horizontal-padding was reduced.