2up page formatting with pages scaled better

So I print a lot of stuff (I can't afford an A4 sized ebook reader) 2 pages per side. The large margins have always annoyed me. Here's the solution.

Two 2 pages per sheet ps document (convert pdf to ps with ps2pdf), with page borders reduced by 1cm:

psnup -2 infile.ps outfile-2up.ps -Pletter -pa4 -b-1cm

-P input paper size
-p output paper size
-b border (margin) change

Changing different borders by different amounts is more complicated but can be done with pstops, and is left as an exercise for the reader.