Total Commander

The most common situation (at least for me) to unintentionally delete something I didn't want is when I have something different in mind (read: under cursor) while some other files/dirs are already selected.

Solution should be simple (at least for me to write:) - when cursor is X (optional & configurable) files/dirs away from any selected object or selected object is not on screen the default action should be "NO". Some additional info. in delete confirmation dialog would be welcomed, but "hardcore" users who ignores confirmation dialogs. If user has turned off confirmation dialog it may appear anyway.

Interesting idea, but also very dangerous. For example, a user who expects the cursor on the left button clicks right arrow or tab and then ENTER to cancel the operation, which would then give the OK in your case...

Well ... thats why it's good habbit to use ESC to escape bad situations instead of playing with TAB or arrows.
User who realised that he didn't wanted to issue delete command is much more careful then the one with mind focused that he know what he is doing. But it can't be helped, mechanical impulses works both ways. For hardcore users confirmation dialogs are there only in case delete command is called by unintentional keystroke.

A bit more complex solution:

Below "Do you really want to delete..." information and above control buttons additional 2 items will appear:
- static text with short information that user might be performing operation on unintentional files
- checkbox with something like "I know" text
Until checkbox is selected action buttons (except cancel maybe) are disabled.

Or you could simply add one more confirmation dialog (should be enough to slap user out of automatic behavior)... but I prefer to minimize amount of confirmation dialogs.

This feature could be turned off by default so only those who will find this behavior to they liking will turn it on.