I have Windows 10 installed on 3 laptops and only 1 of them can be activated. I checked the product keys and they are the SAME. All 3 of those laptops had their own product keys prior to the upgrade. They are also connected to the same Microsoft account. Edit: I just received an email with the following message:
It looks like you've reached your device limit for installing apps and games from the Store on your Windows 10 device. If you want to install apps and games from the Store on another Windows 10 device, remove a device from the device list.
What is the deal here?
Update 7/30/15: I was able to successfully activate on a second laptop. Maybe they fixed it?
Update 8/1/15: Problem seems to be solved. Activated successfully on desktop, 3 laptops, and surface pro 3.