It is considered good practice on *nix based filesystems to chdir to the root so that filesystems can be unmounted as necessary. It is arguable that doing this to most running ruby apps will not have good results as most code out there incorrectly ignores some errnos, however, that portion of the problem is not related to rack. A developer familiar with good daemonization practices should expect this, and indeed it is commonly documented.

http://www.sbin.org/doc/unix-faq/programmer/faq_2.html#SEC16
http://www.enderunix.org/docs/eng/daemon.php
http://www.developerweb.net/forum/archive/index.php/t-3025.html

Fair enough. Would be nice get get some errors back from instead of writing them to /dev/null

Again, closing stdio is part of a standard daemonization process, setup Rack::CommonLogger with an appropriate log file path.