Just FYI,
Upstart is an event-driven replacement for the init daemon
written by Scott James Remnant of Canonical (previously a Debian maintainer)
The original SysV and BSD init systems are very linear, and do not fair well with hot-pluggable devices, or other external system changes
Say you have /usr mounted via NFS
When the boot process hits the mounting of /usr, it could potentially take a little time
(If not done so already, got to initialise networking, get IP, etc.)
Upstart uses events to trigger init scripts, making the whole thing asynchronous, and therefore much more concurrent
You can read the original Ubuntu blueprint from 2006
https://wiki.ubuntu.com/ReplacementInit
Upstart is also, now, used on Fedora and Palm's WebOS