Sounds plausible at first sight. But I doubt that that will be modified because drag and drop Heading "B" behind "C" would let user expect that new order would be ACBD...

@reporter:
is there and Spreadsheet program doing it the way you request? Gnumeric does not.

That's how excel works for example and excel users have no such expectation as you describe:

1. they want to move column/lines
2. everywhere else in the office suite you can move items by selecting them, keeping the mouse button pressed, and dragging somewhere else
3. the column/line selection point is its heading

So having to switch selection point to start dragging is completely unatural and non-obvious

See how confusing the current UI is there:
http://www.oooforum.org/forum/viewtopic.phtml?t=56667