I realize this may require extensive work, but I would like to allow the author to assign any date he/she may wish for a particular entry.  I do *not* want new entries to be put up according to the date and time they were *created*.  Has anyone tried this?

Once you've saved the entry, you can edit the date to whatever you want. Once you save the entry again it will be displayed according to the new date that you assigned it. Some people use this functionality to have their blogs list future events.

Create entry in draft mode
Save
Scroll down there should be a box for the date next to the  Entry status.
- if it only displays a text format date not an editable one you'll need to select customise this page and then either custom (and the editable date box) or advanced.
Input the new date in YYYY-MM-DD HH:mm:ss format
Change entry to publish
Save

(and of course Al-Mah... (gah I can't spell your name ) got it posted faster than me..)