One of the 4 photos page templates for Blurb 10x8 (standard landscape) is misaligned. The top left photo is a little off in the template called "page_44".
The fix is easy: open "Adobe Photoshop Lightroom 4\Templates\Layout Templates\10x8-blurb\basics10x8\templatePages.lua" and search for "page_44". The photo with photoIndex=3 has a width that is wrong and should be changed to 284, like the width set for the other photos in this template.
(This is also the file you can modify to add your own templates, to design pages that are otherwise impossible to create!)