Everyone knows that almost everything you own is replaceable. After a disaster, like a fire or flood, insurance will replace most or all of your possessions. If you're not insured, then you have to start from scratch, but eventually you can earn enough money to get it all back. The only exceptions are the physical manifestation of your memories - pictures, scrapbooks, albums, and so on. There's just no way to recover a burned photograph.
Nowadays, though, people are putting more and more of their pictures in digital format. It's still not perfect; after all, a fire will likely destroy your computer along with your photo albums. for example, I'd hate to lose the dozens and dozens of pictures I took of Washington D.C. when my mom, uncle, and grandmother visited last year, but if my computer dies, they're gone.
Fortunately, we share more of our digital photos, since we can give them away for free. If I lose those pictures, I could call my mom or my uncle and probably have them on CD in a few days. And the same goes for them, since we all kept copies of each others' pictures. Just by pooling those pictures, we've effectively used the old standard "copy three times" backup system, and even provided each other "off-site" backups in case of a disaster affecting the entire area!
But things are getting even better. I added a few photos to my Yahoo! account the other day, and realized that I now have an offline backup system that is virtally invulnerable. After all, Yahoo! (and Google, and MSN, and AOL, and all the others) have their own professional backup systems. Barring malicious destruction, those few pictures I've uploaded are now completely secure from anything short of complete social collapse. I guess I'll be uploading more pictures from time to time...just to be safe.