I just noticed a new "External Content" option on the Gmail Settings page...

External content:

[ ] Always display external content (such as images) sent by trusted senders

[ ] Ask before displaying external content

Learn more: http://mail.google.com/support/bin/answer.py?hl=en&ctx=mail&answer=145919

I guess the Gmail team was listening :-) http://blogoscoped.com/forum/154161.html#id154202