Why do you need one?
It seems to me like Windows8 works perfectly well without it, You can still launch progs, shutdown the PC etc all without 1.
I see it thus. People are afraid of new things, No start button to me means a slightly new way of doing things, Its like getting a new job at Ford when you have been working for GM for 20 years, Sure you still assemble cars but the process is just a bit different, So you learn.
This is also why I think people are afraid to try Linux, Sure it can do anything that you can do on Windows, It's just that it dont look the same, You now have Libre office not MS, Dragon player not Windows media player that sort of thing. They do not look the same but do the same thing. Learning is fun, Well I think so anyway.
Disclaimer: this is my personal opinion
Working with small business clients who range from very knowledgable to very challenged, the largest issue I noticed was the immediate loss of usability without an explanation of what to do next. The Start Menu and Taskbar are the main way people understand how to use their computer, or more specifically, how they organize their open applications and workflow. By loading the Metro UI rather than loading the Desktop by default, Microsoft alienated users and made them feel like "everything had changed". Although change can be a scary thing I am not opposed to it myself, however I believe the issue here was not the change but rather how it was implemented.
For example, on the Metro UI, how do I know how to search for an application I want to run? Without knowing about the charm in the top-right to search I am left with the icons on the Metro UI, which on my Virtual PC is a mess of exe files from one of my program installation. I did not request any of these icons nor have I run half of these programs related to the main one. This creates a feeling like there is no intuitive way to get from Point A to Point B causing frustration. Playing around I figured out that if I start typing it will start searching, but the normal user expects an input area before they give their input, so they may or may not try this.
Another good one was opening pictures for the first time, by default you are launched into the Photos app, and if you were using Desktop Mode you are pulled back into the Metro UI. This seems problematic for two reasons, first a user may or may not be aware that the top-left charm allows you to switch between active applications, so the user may become stranded on the picture with no familiar way to close the Photos application (pressing back brings you back to the main Photos screen). Secondly the Photos app launches full-screen by default, making it difficult to open a picture side-by-side with the app you are running. Sure you can still access it with alt+tab or by cycling through applications, but there is no easy way to find this if you didn't already know.
Granted these issues are geared for the user who uses Desktop Mode on their Windows 8 PC, but so far in my experience nobody is using the Metro UI in production. At several sites we started using the open-source software Classic Shell as an alternative, and some clients went as far as to downgrade back to Windows 7. I am happy to hear that Microsoft is giving people the option back!