Description: Attempting to activate the orca screen reader or activate the assistive technology do not work because after the restart gnome complains about the at-spi-registry daemon not being found.
The at-spi-registryd is installed in /usr/lib/at-spi in arch linux while by-default gnome-session looks for it at ${exec_prefix}/libexec.
I found this page useful http://www.nabble.com/gdm-is-not-starting-the-at-spi-registry-daemon.-t4220844.html
I tried to build the gnome-session package adding:

--with-at-spi-registryd-directory='${exec_prefix}/lib/at-spi'

to the configure line and the problem disappears.

Additional info:
* package version(s) gnome-session 2.18.3-1 at-spi 1.18.1-2
* config and/or log files etc.

GTK Accessibility Module initialized

** (gnome-session:7090): WARNING **: AT_SPI_REGISTRY was not started at session startup.

** (gnome-session:7090): WARNING **: IOR not set.

** (gnome-session:7090): WARNING **: Could not locate registry


Steps to reproduce:

Activate assistive technology in system->preferences->Accessibility, log out gnome, log again in, the error message appears