.gtkrc-2.0

#Create a new file in your home directory called .gtkrc-eclipse

# call eclipse with this command:
# env GTK2_RC_FILES=/usr/share/themes/Clearlooks/gtk-2.0/gtkrc:/home/USER/.gtkrc-eclipse '/path_to_eclipse/eclipse'

# In your Eclipse directory find the file 'plugins/org.eclipse.platform_4.2.*/css/e4_default_gtk.css'
# (there's an * in there, because I guess that the version may change in the future or may be different already).
# In this file there's a CSS class:

#.MPartStack {
#    font-size: 11;
#    swt-simple: false;
#    swt-mru-visible: false;
#}

# And you have two possible solutions:

# 1. Change font-size to something smaller
# 2. Just comment out or remove font-size from this class (works well for me)

# http://stackoverflow.com/questions/11805784/very-large-tabs-in-eclipse-panes-on-ubuntu

# .gtkrc-eclipse

style "gtkcompact" {
    GtkButton::default_border={0,0,0,0}
    GtkButton::default_outside_border={0,0,0,0}
    GtkButtonBox::child_min_width=0
    GtkButtonBox::child_min_heigth=0
    GtkButtonBox::child_internal_pad_x=0
    GtkButtonBox::child_internal_pad_y=0
    GtkMenu::vertical-padding=1
    GtkMenuBar::internal_padding=0
    GtkMenuItem::horizontal_padding=4
    GtkToolbar::internal-padding=0
    GtkToolbar::space-size=0
    GtkOptionMenu::indicator_size=0
    GtkOptionMenu::indicator_spacing=0
    GtkPaned::handle_size=4
    GtkRange::trough_border=0
    GtkRange::stepper_spacing=0
    GtkScale::value_spacing=0
    GtkScrolledWindow::scrollbar_spacing=0
    GtkTreeView::vertical-separator=0
    GtkTreeView::horizontal-separator=0
    GtkTreeView::fixed-height-mode=TRUE
    GtkWidget::focus_padding=0
}
class "GtkWidget" style "gtkcompact"

# Make tabs smaller

style "compact-toolbar" {
    GtkToolbar::internal-padding = 0
    xthickness = 1
    ythickness = 1
}

style "compact-button" {
    xthickness = 0
    ythickness = 0
}

class "GtkToolbar" style "compact-toolbar" 
widget_class "*<GtkToolbar>*<GtkButton>" style "compact-button"