I loved it. There's a sequel, too, which I've also read.
More info on the book here:
http://www.amazon.com/Mysterious-Ben...9453937&sr=8-1
I've been reading a lot of middle grade/YA fiction lately. I also highly recommend Lois Lowry's The Willoughby's (a great send-up of middle grade lit), the Gregor the Overlander series, Cornelia Funke's The Thief Lord, and The True Meaning of Smekday (riotously funny). I just started the Charlie Bone series.