It is not well maintained, and essentially everyone useshttps://github.com/gorilla/websocket.

This was raised as a concern in#17244: because it is in the x/net repository, people attach greater value to it than it really ought to have.

/cc@dsnet

EDIT 2016-12-02: Copying in my better-phrased problem statement from later in the thread:

The problem I see is that the ownership/maintenance story of x/net/websocket is unclear. It may suit your needs, and that is fine! However, it's not getting the same level of support as the standard library or even gorilla/websocket; it has no established owner AFAIK.

Along the lines of#17244, there is concern that it elevates the status and visibility of the package. I've anecdotally heard of it confusing many new users whose needs were much better filled with gorilla/websocket. I have not heard of someone using gorilla/websocket and then deciding to use x/net/websocket instead.