It would be nice if zum could also treat stdin instead of a file.

If only zum could support stdin, then one wouldn't need 100 times more
disk to go from state one to state three:
$ ls -ogs file.gz
496 -r--r--r-- 1 497804 2008-10-09 00:36 file.gz
$ gunzip file.gz
$ ls -ogs file.gz
500131 -r--r--r-- 1 510132224 2008-10-07 13:18 file
$ zum file
file [1000160K]  [1 link]
$ ls -ogs file
51 -r--r--r-- 1 510132224 2008-10-07 13:18 file

I wish I could do zcat file|zum -o newfile

Indeed just
$ zum
hangs waiting for input, but one is not sure what that is about, as
$ echo|zum
gives an error.

To clear up the confusion: when given no command-line arguments, zum reads a
list of files to perforate from stdin.

This behavior will be documented in the next release. (However, I would
still be happy for a patch to perforate stdin, using the common syntax ‘zum
-’.)