I'm having intermittent problems with some services not starting on boot. From what I can tell, when it doesn't work, anything run as a result of the upstart rc-sysinit job doesn't happen.
When the problem happens, I get the following symptoms:
runlevel 'unknown' (from running `runlevel`)
cron not started
apache2 not started
When the problem hasn't happened, these services do start and runlevel is 'N 2'.
The last time this happened was after a kernel update (maybe this makes a race condition happen?). Restarting fixed the problem. The system is running MythTV so only gets restarted when required for updates.