tree expand/collapse keys

For many users left and right arrows are used for caret navigation 
within web pages. Using left and right arrows for collapsing and 
expanding trees/subtress conflicts with caret navigation. It has been 
proposed that we adopt +/- for expand and collapse and not use 
left/right arrows.

I'd like to hear feedback from the group; should we adopt +/- instead of 
right/left arrow for key-based expand/collapse?

Background:
http://bugzilla.gnome.org/show_bug.cgi?id=462156
http://trac.dojotoolkit.org/ticket/4065