If feedback discussions really grab you, you can spend hours and days on eBay's Feedback discussion board. Very entertaining. Loads of responses:
http://forums.ebay.com/db2/forum.jspa?forumID=113

I don't want to take the time to go into the logic and reasons, but what I have decided to do is:
¶ as a buyer, I leave feedback after the item arrives.
¶ as a seller, I only leave feedback after the buyer is happy and leaves feedback.

Robert