Hi JD,
I thought there might be a problem :-)
My gut feeling (read "preference") would be to try to follow the Finder's action as much as makes sense… The problem seems to stem from what happens when it doesn't make sense (and what actually does makes sense in the first place)
1. if Double-click = transfer it should not confuse anyone if you perform a transfer of all selected items, remote or local (is this not what happens now? I personally have never set that option)
2. Double-click = Edit. Edit remote files and ignore remote folders. Locally, why would it not make sense to open local files in the editor? If you cmd-down in the finder it will open all selected items, which would usually mean "Edit" for files and "open new finder window" for folders. You don't want multiple windows in YummyFTP, so you might choose to do nothing for folders, but maybe there would be some value in simply throwing an open event at the finder (for local items) and letting it deal with whatever would normally happen (i.e. let it open new finder windows - that is what the user asked for after all)
3. Double-click = open URL. Maybe doing similar to 2. could make sense. If the user wants to throw files at Safari (or whoever), why should you discourage it? Doesn't make much sense for folders unless you expect to browse them. (when I drag a bunch of files and folders onto Safari it opens what it can and ignores what it doesn't like - I'm not offended by that)
You can probably tell that I'm thinking out loud here, but it seems to me that you could treat cmd-down on local items by simply throwing an open/openURL event at the Finder and letting it deal with it - maybe even to the point of causing it to open new Finder windows.
For remote items I think it would be appropriate to perform the selected-in-preferences double-click action on all items where it makes sense and ignore it for items where it doesn't. If you simply revert to extend selection (which is actually shift-up/down BTW) when multiple items are selected then you're losing the ability to operate on multiple items instead of (quite reasonably) ignoring the action for those items for which that action doesn't make sense (i.e. folders - opening more than one folder is not really feasible).
In order to cause minimal confusion due to changing the behaviour might I suggest a fourth item in the "Double click action" preference… "Finder-like"? or maybe that is overloading the preference too much :-)
Hopefully that makes some sense. Kiwi
P.S. Apple changed the shift-up/down behaviour recently such that it no longer "extends" the selection in all cases. If you start with shift-down and then use shift-up the old behaviour was to extend the selection to include items before the first one. The new version reduces the selection - much like it does in most editors (handy for when you've selected too far and just want to deselect the last couple). Basically it sets an anchor at the first item and selects from there to the current "position" (so shift-down x 2 followed by shift-up x 3 ends up selecting the first item and the one before it only).
P.P.S. cmd-up does nothing when you are not in an enclosed folder - just one example of ignoring meaningless user input. Just saying… :-)
