I like how when I hover over an image a little transparent box appears. In the box there is a caption and the name of the account. On the right there are options to favourite, comment and zoom. I think this is really good.
I’m not sure yet if this would be needed on my site but I think its a neat and intelligent way of making the site interactive. By having all the options appear like this, it doesn’t ruin the nice clean, simple photo album layout. Well done flickr.