I filed a bug called "Add context menu to splitter itself to 'Change splitter
orientation'", at http://www.jetbrains.net/jira/browse/IDEA-1587, and it
was marked WONTFIX. I think this, along with double-click behavior, would
be very intuitive, and would be one of those little UI features that sets
IDEA apart from Eclipse or NetBeans.
I'm not complaining about the WONTFIX, rather I think others would agree
that this would be an intuitive way to change the splitter orientation. If
enough people agree maybe it will be implemented.
So, what do you think?