Linux Fedora 15 (Local en_US)
I use metric sizes paper A4, A3, B5, etc.
When I print to CUP-PDF, the paper size is limited to Letter (that's the unique option).
I am not positive, but it looks like a Freemind limitation.
With any other applications, I can set a different paper size using CUPS-PDF.
To print to A4, the workaround I am using is to select any physical printer. I can set the paper size. Print to file (.ps), convert the .ps to .pdf using ps2pdf command.
It would really come in handy to print directly to CUPS-PDF, if I had the option to change the paper size.