As you probably already know I use Flickr to manage and archive all of my images. I usually get at least one email forward from friends or family with photos in it. Instead of downloading these attachments and re-uploading them to Flickr I’ve set up a filter in Gmail to auto forward all image attachments to my upload by email flickr address. Of course I set them all to private by default.
Now whenever someone sends me photos they get saved (privately) in my Flickr. Keep in mind the Flickr upload by email feature can be flaky and isn’t designed for huge files or large numbers of files. I also do the same thing for documents and spreadsheets except I use Google Docs instead of Flickr.