In Acrobat 9 Pro, there was a Portfolio layout called Grid with File Preview. We use it as our primary layout for PDF portfolios because it allows users to rapidly view PDFs within a portfolio. This was our primary reason for using Portfolios. Unfortunately, this important feature was removed in Acrobat X Pro resulting in clunky and very slow PDF viewing.
Adobe needs to immediately reinstate Grid with File Preview into Acrobat X Pro. Until this happens, I will continue to use Acrobat 9 Pro.
I encourage everyone to use the Feature Request/Bug Report Form to submit this as a Bug. Unless everyone complains, nothing will happen.
Check out this free layout and instructions for installing. This is just what I've been looking for since we upgraded to Acrobat X. My attorneys hated reviewing thousands of PDF files that looked like flying cards. http://blog.practicalpdf.com/2012/07/grid-with-file-preview-pdf-portfolio-layout-available -now/