I got one of those notices on my Win7 Pro pc that I use as my main computer. I am going to wait as we have 1 year to upgrade for FREE. And from what I read, if you upgrade within the first year, it will be FREE forever. I don't know if that will be the standard edition though and then to upgrade it will cost you as there are rumored to be 10 different versions.
My wife has Win 8.1 and I will use her pc as the beta tester.
I also have a Win 8.1 pc from HP that I bought in a hurry a few years back to test one of my apps to make sure it worked on Windows 8. It is a plain Jane vanilla pc and I will turn it on and let it watch for the update message and use that too for a beta tester pc. I am not sure if the update works with reseller pc's (Dell, HP, etc) as opposed to home built pc's which is all I have with the exception of the hurriedly purchase HP Win 8 pc.
schemer
added: I like to keep one of every OS in a running condition for my own testing and work. I have Win95, Win98, XP, Vista, Win7, and Win 8.1 now. Every time I build a new pc the old one gets added to the network, with the exception of Win95 and Win98. Those last 2 don't ever get turned on anymore, but I keep them just in case.