I added a note on vertical toolbars at:
http://developer.gnome.org/projects/gup/hig/draft_hig/toolbars.html#vertical-toolbars

However much I tried, though, the best advice I could come up with is
"it's almost always better not to use them" :)  If anyone has some
better advice, feel free to comment....

It was pretty trivial to remove the vertical toolbar from
GnomeMeeting. It had far far far more toolbar items than it needed.
Not sure its a very good example. 

Actually, not sure there are any good examples, because my personal
feeling is that we should avoid the "toolbar bloat" ala Microsoft
Office. At some point toolbars lose their usefulness because they have
too many items, and you might as well encourage menu use instead and
leave the toolbar for the truly common items.

If the user wants to turn on 20 toolbars and make some of them
vertical, they can go right ahead, but I don't think applications
should have more than one or two, toolbars visible by default.

marking fixed