I just learnt from a vimcast (#18) that one can format paragraphs justified. This seemed very attractive to me, but I had one problem with it: I use double spaces after the end of sentences to distinguish periods from abbreviation dots. Using set cpo+=J, par does not preserve these double spaces; can it be made to?
Formatting with par and justified option
formatting
(Not to let this without an answer; even if a short one) A quick digging on the internet shows the right par option: g1. To quote the source:set formatprg=par\ 72q\ g1   Use par for gq. use gw for internal formatting                             g1 preserves double spaces after periods.