This is a summary of an ongoing discussion on kde-look FYI:

It would be nice to be able to print documents from within applications 
with a single click on a toolbar icon, bypassing the usual printer 
configuration dialogs.

KDE's style standard says that the function of toolbar icons should 
match with an item in the menubar. Having a toolbar icon with a 
function which is slightly different than the function present in the 
menu is confusing for users: Users expect that the toolbar icon behaves 
the same as the menu-item.

If a toolbar icon provides "print directly" functionality it should be 
shaped significant differently from the 'normal' print icon. 

Cheers,
Waldo