On the XO 1.5 with Etoys 4.0 using the <Ctrl> key as the Cmd key:
<Ctrl>-1 : sets font to size 5
<Ctrl>-2,4,6: do nothing
<Ctrl>-3 : add's curly brackets around the selection {Text}


On Mac running 4.1 Beta behaves as follows:
Cmd-1 5 point font
Cmd-2 9 point font
Cmd-3 12 point font
Cmd-4 15 point font
Cmd-5 18 point font

Documentation in Command Key Help (Cmd-, -> help -> command-key help):
Cmd-1 9 point font
Cmd-2 12 point font
Cmd-3 18 point font
Cmd-4 24 point font
Cmd-5 36 point font
Cmd-6 color, action-on-click, link to class comment, link to method, url
        Brings up a menu. To remove these properties, select
        more than the active part and then use command-0.
Cmd-7 bold


Also the font is chanced to BitStreamVeraSans on all platforms when using these keys