Who's using them? What is your impression?
From the EB Literature:
"Engineered to maximize output and clarity, Ernie Ball Cobalt Slinky Guitar Strings are the latest innovation in string technology. Seeking to provide guitarists and bassists with a new voice, Cobalt strings provide an extended dynamic range, incredible harmonic response, increased low end, and crisp, clear highs.
Cobalt provides a stronger magnetic relationship between pickups and strings than any other alloy previously available. Cobalt Slinkys are also soft and silky to the touch, making string bending a breeze."