I use Flickr for 2 main reasons
- It enables sharing my photos with my friends and family
- It serves as an online backup of all my Jpegs
I originally started using Flickr for #1. However, with hard drives as they are, and after having lost a complete drive a few years ago (no service or software could revive it long enough to get the data off it), I decided a while back that storing stuff online was a great idea. Though I use RAW+Jpeg on my Canon dSLR, I can only back up my Jpegs (currently -- and in fact I haven't found anywhere that provides good, free online storage of big photo files). That's okay; I'd rather have my Jpegs backed up and not my RAW rather than have nothing at all backed up online.
By the way, I also make regular backups of my data onto both external hard drives and DVD/CD. I'm a little paranoid now.
Anyway, here's a post for Flickr noobs. Flickr has lots to offer but it's certainly not the most user-friendly site on the web.
Newbie's Guide to Flickr | Webware : Cool Web apps for everyone