Joel Zumaya has been great. He's fun to watch. And Doug Mientkiewicz covers all of this in this article by ESPN's Jayson Stark:
If your stadium radar-gun board doesn't reach triple digits, you'd better hope the Tigers don't come to town -- because rookie infernoballer Joel Zumaya hits triple figures on the MPH board about as regularly as Jeff Gordon.
Just in one May 30 outing against the Yankees, he threw five pitches at 100 MPH and five more at 101. But the best description of what it's like to face him came from Royals first baseman Doug Mientkiewicz, after having to hit off him in the shadows during a day game:
"He was throwing 100 mph in the dark," Mientkiewicz told the Kansas City Star's Joe Posnanski. "All you can do is swing early and use Jedi mind tricks."