You must know that October 26 is the first day of availability of Windows 8 and I can’t imagine not downloading it immediately at the $40 price tag. Just a friendly PSA that you should backup your PC (or at least back up your media) just to be sure. It’s been well tested by why risk it?
And as a reminder, here are the terms of the $40 promotion. Yes it’s cached because MS is updating their site to be all Windows 8ish. Simply put, you’ll download the update assistant that will confirm your PC and software is good to go and then you can choose to auto-install or download it for creation of a USB or DVD (I’m going USB). Expect the upgrade process to take about 15 minutes if it’s like the betas. It’s unclear at what point you buy the license to Win8 but I’m sure we’ll all figure it out. I’m damn excited.