You can use "j" and "k" to go to the next or previous item in a lot of web based applications, including Flickr, delicious, Facebook, Google+, Gmail... try it. Try it anywhere else - it's probably supported by some applications you use that you didn't know supported it.
Web services copied this from the Unix world, where it was popularized by the vi text editor, nethack, and a bunch of other programs. If you used a Unixy text mode email program like elm, mutt, or pine, then you had j/k for up/down.
Did you know that "j" and "k" are often used as up/down or previous/next keys?
Yes, I use j/k for up down in some application(s) often.
I know this, though it's not something I use much currently.
Seems familiar... you just reminded me, but I think I knew.
Doesn't sound familiar.