Exactly how does one navigate through ubuntu's startup files?

I understand that there is a switch from init.d to init in Ubuntu. Init.d was fine for me, but I can see and appreciate the change. I am also incredibly thankful that the config files are not foul XML, like launchd's are. Good ideas.

However, using maverick, I still see an awful lot of stuff in init.d. I had thought that upstart was the way forward. I am certain that upstart + init.d is not as simple as either one alone.

So how do I determine the startup procedure, or where to look for files to control some server?

EDIT: More to the point, I guess I'm asking how does the interaction between upstart and sysvinit work today? I am suspicious of the wiki, much of it seems to be from older versions.