I'm a fan of callouts to add annotations to a picture. 
I'm also a fan of connectors, since they allow me to reshuffle the elements
of my pictures to fit the available space.

What I miss is the possibility to attach the point of the 'arrow' of a
callout to a glue point of another object, so I don't have to relocate
the arrow head after shifting the text part of the callout. Perhaps connected
to that, I frequently find myself trying to select a callout using a
rectangle selection to find it did not get selected because the arrow was not
fully included in the rectangle. I'm aware of the fact that this would
probably confuse old-time users, so maybe it should be a new type of callout,
or a new type of connector ('extends text box object'  ???). The new type of
callout can then be constructed from a normal textbox and a connector.