Ferraro is not particularly good at anything defensively save for blocking shots and breaking up chances. He's not particularly good at exiting the zone or preventing zone entries. He also doesn't really generate much offense - of course, being paired with Burns for two years may skew the data somewhat (of course you're not going to do much offensively when you're partner is Burns), but watching Ferraro doesn't exactly indicate he has a ton to offer there anyway.
He does eat a lot of minutes, though, and what he does do well has value. Third pairing is probably reasonable, maybe the supporting half of a good second pair player. He's probably overpaid by $1 million, which isn't awful (every team is overpaying some people) save that the Sharks are already overpaying Vlasic by about $6.3 million, Karlsson by $3.5 million, and Simek by $1.5 million. It's also of course possible that Ferraro has room to grow.
I'm basically not going to worry about Ferraro too much, but it does seem that he's not going to turn into anything more than a #4 defenseman and is best suited as a #5-6 but is forced to play above his abilities right now.