Suspend on laptop lid close has never worked on this install and it appears that it is not due to the really common bug described here when acpi improperly expecting a laptop to be docked.
Instead it looks like the power manager is not catching the lid close at all. The lid state is being stored in /proc/acpi/button/lid/LID/state and tailing that gives:
sarai@ninjacer:~$ tail -f /proc/acpi/button/lid/LID/state state: open tail: /proc/acpi/button/lid/LID/state: file truncated state: open
But closing the lid with that running should change the file, no? Nothing additional gets written when I close and reopen the lid.