I think double clicking (and dragging) is supposed to have the same selection rules (what is a word, where the selection stops, etc) as ctrl+left/right, but I've yet to encounter anything that does. It drives me nuts.
Those keystrokes have never had a standard behavior that you can rely on. As a result, since I use a wide variety of applications on a wide variety of operating systems, I've never incorporated them into my workflow. I can't remember the last time I actually used either of them.
