DrakeFS :
At $200, this is tempting. Becoming a lot easier to justify it as a 3rd monitor.
It's not really like a monitor though. Oculus Go is a standalone device, more like a phone or handheld game machine. From what I can tell, you won't be able to hook it up to a computer, and are limited to the performance of the built in mobile hardware it ships with. Plus it only does 3DoF tracking. It basically has the same VR functionality as a mid-range smartphone in a plastic shell, and runs the same mobile software.
PC connectivity would be a feature I would want to see in a device like this though. I don't see much reason why they couldn't add the option to connect a tether for PC VR without increasing the cost much. And for that matter, if they can sell a device like this for $199, it seems like it wouldn't cost much more than $100 to include standalone mobile VR functionality in higher-end PC VR headsets. We'll likely see these standalone and tethered devices merging soon enough.