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So just I ran some inurl: operator tests and I'm not coming up with any positive evidence. If I were forced to guess right now, I'd say they're not using it.
Anyway I believe that Google's robot easily checks for case sensitivity by requesting the same URL that was ok with different case.
One canonical form (e.g. all lower case) should return the content along with a "200 OK" status, and all other versions of the URL should return either 404 or a 301 redirect to the canonical form.
Be very careful with this.