I found Flickriver a few days ago and I’m already using it regularly. It’s an incredibly simple ‘skin’ for Flickr. Its point of difference is that it loads all the photos you want to view on one page. As you scroll down it loads more photos. This means you can load your contacts photos and all you’ve got to do is scroll down till you see a photo you’ve seen before. No more opening multiple tabs or skipping photos because they didn’t look great as a thumbnail.
They also have a bookmarklet (click tools to get to it) that you can hit when you’re on a Flickr page you’d like to view in Flickriver. So if you get to a set on Flickr and you’d like to look at all the shots. Instead of opening them all in new tabs, hit the Flickriver bookmarklet and they’ll all be displayed in one page, on black.
Clicking on any photo in Flickriver takes you straight to that photo on Flickr if you want to comment, favorite et cetera.
