I actually have three feeds:
-friend's photos
-comments on my photos
-comments made after my comments on another photo
Real photosharing penetrates demographics where people don't understand computers, not just people who don't understand RSS. My point about RSS is that Flickr is the best for non-technies and techies alike.
1.) They have a pretty good multi-file uploader, so you can take a whole directory of files and upload them at once.
2.) It's free. Many of the other sites with #1 require that you pay for it.
3.) You can tag your friends, and a notification in their news feed will pop up saying they've been tagged in a photo. And all of their friends will see it, usually leading to tags for people you don't know.
4.) Enough of my friends are on it that #3 is useful.
A lot of this is network effects - I think Flickr has all of the above, though some may be premium features. But FaceBook has a critical mass of people that check it regularly, which makes 3 & 4 a lot more useful. If I post to Flickr and tag my friends (can I do that?), there's no guarantee they'll see it.
2.) Photo-sharing. As of now, it really seems to be the best photo-sharing app on the net.
3.) Making plans to meetup offline or catch up with old friends. This seems to be the most common use of the wall (and to a lesser extent, poke/superpoke), though I gather some other social groups use it for actual silliness.
4.) Scrabble.