Being inspired, I ended making a GDM login theme from a 1080p Blu-ray rip of Five Centimeters Per Second:
It is designed for my 1920x1200 resolution laptop running Ubuntu 8.10 Intrepid. Modified it off of this Serial Experiments Lain theme. Source GIMP XCF file is available inside the tar.gz if you want to modify it.
It's not the greatest, but it really didn't take much work. I added some sharpening and adjusted the colors and saturation from the source video screenshot, but that's about it.