When it comes to designing customized layouts and complex content-rich pages, few Drupal modules can match the flexibility of Panels. It shatters Drupal's traditional "Region/Content/Blocks" divide, giving site managers the ability to build custom layouts and enforce consistency across different types of pages.
Unfortunately, the "variations" system that Panels and its companion module Page Manager use can be cumbersome; developers and advanced site builders can master it, but managing huge numbers of different layouts can be a pain. This is particularly noticeable when each individual node on a site, or even of a particular content type, needs to have its own special layout or mix of page content. Wouldn't it be great if there were some way to give some editors and content creators control over the Panel layouts for just the nodes they create? That's exactly what the Panelizer module does.
Activating Panelizer is simple; its settings screen allows you to "panelize" any content type, piping its output through the Panels layout engine. In and of itself, that's not much different than overriding the standard node display page using Panels' normal Page Manager interface. With Panelizer, however, authors creating panelized node types can change Panel layouts, page content, and other Panels settings individually for each node they create. Administrators can choose which Panel layouts and Panel content types are valid for each node type, so writers and editors aren't overwhelmed with options that don't apply.
Once everything is in place, nodes can be created as usual; once they're posted, however, authors can click a "Customize This Page" link that utilizes Panels' in place editor. Dragging chunks of node content and related widgets around inside of the normal page design, then clicking save, is all that's necessary to customize a Panelized node. If you're used to hand-theming to achieve those effects, or laboriously constructing manual override variants using the Page Manager module, it's nothing short of amazing.
Panelizer is currently in beta, but is already in use on a number of large-scale sites including the NBC iVillage community. A developer snapshot release is available for Drupal 7. While it's definitely on the bleeding edge of site building, Panelizer is a genuine leap forward for Panels and complex Drupal designs. Check it out!