While I've admired "modern" quilts and have several books, this is the first time I've taken a class or tried this genre of quilting. It was fun, but does involve thinking a little differently about your process. Modern quilting (as I see it) includes a lot of negative space (background), simplistic design elements (at least they may appear so), more solid colors than traditional quilts, and clean shapes and lines. As Jacquie put it, they have their roots in traditional quilts, but with a different interpretation. And though they may look simple, they are less so when you start looking at the construction.
Yesterday's class was called Scrappy Improvisation. We started out by making blocks from scraps (or yardage) that consisted of squares, rectangles, wedges - just random piecing; no specific sizes or shapes. The difference between this and other methods of free-form piecing was that we incorporated pieces of the background fabric as well for "inflow" - so the background would flow in and out of the blocks, making them seem to "disappear" into the background.