You can find the actions through the Tips at the top of the site:
Where can I download Katie's action that resizes scrapbook pages for Shutterfly books? - Digital Scrapbooking Tips DesignerDigitals
Lynda, I just upload my 12X12 layouts saved as 300 dpi jpgs to Shutterfly. If you upload, you can make 12X12 or 8X8 from the same jpg - it will automatically scale it for you. As long as you have made sure to not put any important text or item within 1/4" of the edges, you shouldn't have any problem with trim. Use their templates for the cover though as you can't just upload a 12X12 for that and have it work nicely.