Salesforce use this in their Lightning Framework. I've not gone beyond the surface of that framework, but I've found its use of proxies adds friction to development. Trying to debug in the browser, anything other than a primitive results in a looking at an empty Proxy object - I believe this is a deliberate choice behind the framework in the name of security. But it makes it much harder to discover what's in an object - if you don't know the name of a property, good luck getting it.

Note that this is either due to how the framework uses Proxy, rather than Proxy itself, or I'm doing it wrong and should do more reading up on it. It really could be the latter - given my level of experience and knowledge, I thought hard about posting this comment!