While it doesn't enforce the guidelines, their Closure Compiler enforces the variable types and encapsulations declared in the JSDoc comments with warnings. http://code.google.com/closure/compiler/

On another note, a Google engineer argues against Crockford's arguments for functional inheritance while pitching the benefits of the Closure Compiler and Library: http://www.bolinfest.com/javascript/inheritance.php I find his points are well made.

Also check out Bolin's "Closure: The definitive guide" book, available as a rough cut. A great book indeed.

If guidelines were meant to be enforced, they'd be syntax.

not necessarily ... official language standards bodies might make decisions much more slowly than individual hackers or groups, and even when a feature is officially baked into a new version of the syntax, it might take compilers/interpreters several more years to all implement them properly. there's definitely a need for good lightweight static checking of guidelines in IDEs

No, because guidelines can be overridden when there's a good case for doing so. Not so with syntax.

Agreed. "Style is only necessary where understanding is lacking." - Doug Hoyte

well said

You don't need an IDE for that, but some code analyzers do give you hints/warnings. There's something for Python (google it)