I've switched a number of books over to 8.5" x 11" format. Although this is not a traditional size for computer books (most computer books are around 7"x 9"), moving to 8.5" x 11" reduces page count for printing conserving resources and reducing cost. I've found it much cheaper to print books on 50-weight 8.5x11 vs. 60-weight 7x9. While, I'm comfortable with DocBook XSL, I dread FO, and the idea of configuring the XSL to create two-column FO is very possible, but wasn't something I wanted to jump into without first evaluating InDesign's support for columns.