Greetings from Viovio!
There is an automatic trim that occurs during production to ensure that all pages are flush. This trim is approximately 1/8 inch on all sides. We suggest that all vital content is kept within .25" from all sides, and consider this the Caution Area. We do not guarantee any content that is not within the Red crop guide (.25") / Caution area. You can learn more about this here: http://www.viovio.com/wiki/Cropping+And+Bleed
All vital content like text and faces should be kept within the Red Crop-guide for all standard size books. The Pink Crop-guide for mini-books is more aggressive due to the the mini-books small size, and therefore requires a more aggressive crop-guide.
Here is a great screencast that will explain all of our crop-guides: http://www.youtube.com/watch?v=E8Ksz1k8Djs&feature=mfu_in_order&list=UL
You can view your project in reference to the crop guides most accurately at the Layout Preview in Step 3:
For the Layout Preview:
(The crop guides are able to be viewed or removed by simply clicking or un-clicking the "Show Crop Guides" at the top left of the preview.)
The Red crop guide is for standard size projects (9x7 or larger)
The Pink crop guide is for mini-books (anything smaller than a 9x7)
For the Flip Preview:
The Flip preview offers 1 single yellow crop guide that is both the Red and pink crop-guide combined, and is therefore more aggressive than necessary for standard size books. For most accurate crop guides when considering your work, please use the Layout Preview