A while ago I stopped using either Aperture or iPhoto to manage my photos and switched to Lightroom. Pretty much the only downside of switching was the lack of PhotoStream import. This lead to me having a bit of a poke around on the filesystem and see where the Apple products were getting the photos from.
It turns out that once you have installed either Aperture or iPhoto the iCloud system preference lets you enable PhotoStream support. What this actually happens in the background is some system service is enabled which downloads the photos into a directory under ~/Library. I intended to keep Aperture installed, so I figured I could just write a short bit of code to walk this directory, pulling out photos and putting them into a directory of my choosing.
I’ve put the script up on git hub, which you can find here. Feel free to copy it and use it, drop me a line if you have any issues.