This hampers nfs usability, for example:

$ fsysopts ./
/hurd/nfs [...]
$ cp -a /bin/true ./
cp: failed to preserve authorship for `./true': Operation not supported
$ ./true
$ /lib/ /bin/true
$ /lib/ $PWD/true
[...]/true: error while loading shared libraries: [...]/true: failed to map segment from shared object: Error 1073741869

IRC, freenode, #hurd, 2012-03-14:

<civodul> i just realized that uses mmap unconditionally
<civodul> so executables or shared libs can't be used off a netfs-based
  file system
<civodul> that's annoying
<tschwinge> civodul: Do you know what it takes to fix libnetfs?  I have no
<tschwinge> Never looked at it.
<civodul> tschwinge: implementing io_map
<civodul> but i think the idea is that io_map typically isn't convenient
  for network file systems
<civodul> which is why it doesn't have it
<civodul> the GCS says "thou shall not require mmap" ;-) Analysis to be found on mmap page.