I wanted to harness Media Center's ability to display photos, but don't actually store anything locally; a while back I made a call to use Flickr for my photo storage, thus ensuring that I had an off-site backup of all my photos.
This was something of a problem. Flickr don't actually give you an easy way of downloading all your images, but this is what I wanted to do to use them with Media Center. Ashleigh had suggested using Little Syncr, but that app doesn't actually download any images from Flickr in the first instance, but rather syncs everything up moving forward.
Enter FlickrDown. This little app has handily downloaded all of my Flickr images to my local machine, and I can now display them using Media Center. I'll have a play with Little Syncr later to see if that's a good bet for future Flickr activity 
