Marshall - 8:30 pm on Mar 27, 2012 (gmt 0)
If you are hiding CSS/JS from search engines, you probably have something to hide. Possibly blackhat.
This goes back to what I said about searching for display:none. I will freely admit I use that on elements which the user cannot access, but not for black hat purposes. Occasionally I want to hide something that should only appear when the page is printed, say an alternate header. Am I to be penalized for not wanting my visitors to have to print a large colorful graphic when a small black and white one will do? Is Google going to compare my screen CSS to my print CSS? Or maybe I want to hide something when a handheld device is used. Am I to be penalized for trying to make my regular page fit a small screen? My sites are built for the convenience of my visitors, not Google bots.
And if people want to black hat, that is still easily accomplished with detection scripts.