It's becoming less usable (see: JS classes, prototypes were separated in some but not in others) and the information on it isn't keeping up with standards at all. It might be fine for people who are working on browser builds as of about 24 months ago, but it is woefully inadequate for anyone who wants to use something that is even in a draft state or considered stable.
A quick example: look at document.cookie. They are referring to DOM2 information. It's undergone some (slight) changes in HTML5. Nothing is referenced, even though that section is relatively stable and marked as safe for implementation. That's a 2000 spec vs a 201x spec. Nobody's even gone in and pointed out that this has changed in HTML5.