The first time I held a Kindle in my hands I thought, this might be a game changer - at least until you start reading scientific papers which have a two column layout. Which is great for printed media, but as soon as you want to read it using a device zooming won't help. Thanks to a hint of Christian I found this blog entry from Steven Wittens presenting the idea of cutting a two-column PDF page into 4 pieces. The complete program was written in Python and a no-brainer to execute - if you love the command line...