The following is a list of known issues with MATE on Slackware:

Fri Mar 22 16:45:28 UTC 2013
Mate-screensaver in /testing doesn't seem to work -- at least, the locking
feature does not seem to work in my testing.  I tried it with xscreensaver
disabled and also uninstalled but it never kicked in.  More testing is
necessary.

Fri Mar 22 16:44:59 UTC 2013
Help menus and help buttons do not work -- this is a known issue per a MATE
upstream developer and scheduled to be fixed at some point but not in the next
release (1.6).

Fri Mar 22 16:43:36 UTC 2013
Working to determine whether mate-polkit is necessary.  According to upstream,
it is, although it results in duplicative polkit actions when a USB stick is
inserted, for example.  Disabling polkit-gnome in the "Startup Applications"
is a workaround until more testing is done.