Tim -
Most *nix systems don't read it by default, neither will classic Mac OS or OS X. Or rather, won't unitl KOffice, AbiWord, OpenOffice, or Office for Macs is installed (OOo is a pain to get working on OS X)... Also, as bryanthompson mentions, your formatting/fonts/etc is not guaranteed. There is a reason the IRS uses PDF files for the downloadable docs
