Oh, one point - after 90 days the items disappear from your feedback list but you can still leave feedback by mangling the URL. This is a way to leave negative feedback while knowing that the other person is highly unlikely to be able to leave some in retaliation unless they know the trick.

The URL format is:
http:// feedback.ebay.co.uk/ws1/eBayISAPI.dll?LeaveFeedbackShow
&item=XXXXXXXXXX&useridto=THEIRID&useridfrom=YOURID&transactid=0

Gareth