gravatar URIs

Short and simple: http://en.gravatar.com/avatar/<md5 hash of email address>?.
e.g. echo -e 'bob@email.com' | md5sum gives: c961431faea38ed65bfd982cf2e31bd0. Optional add-ons are size (s=<Number of pixels>), content rating (r=<g, pg, r, or x>), and default (d=<escape encoded URI of an image or one of identicon, monsterid or wavatar>).
great place to do something akin to the 'imitate a lotus notes password entry trick'.