Upstart wasn't the first init replacement, but it seemed to me that it's the most complete, with backwards compatibility, service supervision etc. Scott was able to look at the designs of launchd, initng, daemontools, smf, and in a way, his own - early upstart has seen a major deployment in Ubuntu, and it seems he learnt a lot from the early experience. Now it's seen adoption not only on Ubuntu and Fedora, but also on the Palm Pre's WebOS and Nokia's Maemo.
I'll be glad to be able to move away from racy, crufty boilerplate shell code for initscripts. Of course I suspect it'll be a while still until all the Debian packages with initscripts are converted to upstart jobs, and I'm curious to see what changes Debian wants to introduce in upstart.