Here’s a shell function to add to your profile that makes it easy to view man pages in OS X’s Preview.app:

pman() { man -t "$@" | open -f -a /Applications/Preview.app; }

If you care about window titles (and temporary extraneous temp files) you can do this instead:

pman() {
    local TEMP_DIR
    local TEMP_FILE
    TEMP_DIR=$(/usr/bin/mktemp -d "/tmp/pman_temp-XXXXXXX")
    TEMP_FILE="${TEMP_DIR}/manual page for ${@}.ps"
	
    man -t "$@" >"$TEMP_FILE"
    open -a /Applications/Preview.app "$TEMP_FILE"
	
    # clean up the temp directory after Preview is done with it
    ( (sleep 30; rm -r "${TEMP_DIR}") & )
}