Seam Carving for Content-Aware Image Resizing
Update: Video Thing has some comments and links, including one to "An Informal Catalogue of Slit-Scan Video Artworks."
Update 2: In Imaging heavy hitters join Adobe John Nack details a number of interesting additions to the Adobe staff.
Update 3: Picutel is releasing a PS plug-in for this sort of image resizing (September).
Update 4: another tool Liquid Resize was noted in comments, and Studio Daily added info in Seam Carving for Content-Aware Image Resizing.
Update 5: CNET added a newer video from the developers.
Update 6: Gantico tested Resizer, a Flash app in this category; see Test: my first liquidly resized picture.