After following the Try It Out on page 470, the GridView on Reviews.aspx works correctly in Design View - ie the Test Query showed the correct results.
When I view the page in a browser, I've tried Firefox 21.0 and IE 10, the Grid doesn't display. Furthermore when I view the generated HTML, it's not there either!
I replaced my Reviews.aspx and Reviews.aspx.vb with the ones from the book's download - still the same thing.
I am not having this problem with the GridView on the Genres.aspx page.
Truly stumped, any advice much appreciated!

Figured it out. When I removed the WHERE clause it worked OK. I went back to the DDL and I had the Data Source set to "Specify a custom SQL..." rather than "Specify columns..."