So I am not a Masterfile contributor but their web site almost wish i was a Masterfile photographer!  I saw their new site(maybe not so new anymore) a few weeks ago and thought the site work about as perfect as it gets.  I love the clean white look with the bright retro brand and the scrolling horizontal thumbnails is pretty slick.  The thumbnail system really allows you to see more images faster... and that is key.  Also dig how when you find an image it can immediately give you the similar or other frames from the same shoot.  Pretty nice!  A another item that is nice is the toggle feature between the RF and RM options. 

Well done Masterfile!

Just a few more comments on this site.  I talked to the some masterfile people and there are a few key features i left out... one of which masterfile has a patent on.  It is called Visual Matching.  Basically you can now visually match an image with something completely different!

Also you can zoom into images online.  Once you click on an image and it opens up large on the left side of the screen, there is a magnifying icon underneath and you can zoom in.
Also try randomly selecting (clicking on) any 4 or 5 images, then on the last image you click on (it will be large on the left hand side), you will see a back arrow to the left of the image, this will remember everything you just clicked on and bring back the similar images without changing your original search area.  There is a History tab that will log a thumbnail of each image and store it by which day you were searching.
 
I we leave a video demo link that you can watch as well - turn on your speakers: http://creative.masterfile.com/endlessmedia/howitworks.php?lang=en_en