According to my mother, this book was probably the source of my own preschool foray into imaginary friend-dom. I had completely forgotten about it myself, until a few years ago when the mention of Guy-Guy, Mr. Dobie, and Bickerina brought back the memories of that small library book with its crinkling plastic cover...and my own trio of misbehaving, invisible visitors.
I absolutely love some of Charlotte Zolotow's classics (I Know a Lady and Over and Over) but this one didn't compare. My two-year-old enjoyed it so I gave it three stars instead of two.