I installed windows 8 as an OEM on my originally windows-7 running machine, and I don't have any issues whatsoever. No start menu? Oh boo ho, get used to the charms menu and you can search again. You can also just right click on the 'start button' to get a dropdown with all the things the old start menu had (personally don't use this, just learned how to use the new ui instead). Now that I am accustomed to the new stuff, I can reap the benefits of having integrated Skydrive, synced settings across four different computers (actually impressed at how well this works), and overall improved performance.
Kaph is also full of it. The new task manager is far better, you can see measurements of not only Cpu and memory usage of every process, but disk usage and network utilization as well. There are literally no downsides.
Sorry for being completely off-topic, but I had to type this as Kaph just needs to get his head out of the ground. He falls under one of those 'me no like change' caveman people.