In addition to the enhanced Vanishing Point capabilities in its cheaper sibling--the ability to create linked planes at odd angles--Extended allows you to measure the planes and angles as well as export the meshes to DXF or VPE (After Effects). You can import a few popular formats of 3D models and edit any embedded texture maps; there are some basic rotation controls, coarse rendering options, and some odd lighting presets (it will load lights from the file, however).
However, if Adobe intends this to be a useful tool for creating presentation materials using 3D objects--can you say Acrobat 3D?--it needs more high-quality renderers and light presets, plus better visual feedback as to whether you're manipulating the camera or the object. The cross-section view is nice, but a reference axis floating in the object space would be really helpful. You can apply filters to 3D objects via Smart Filters, which I have to admit is very cool for producing "artist's rendering" views of a model.
Extended also contains some refugees from the now-defunct ImageReady, including its frame-based animation tools. Adobe has expanded the animation to include a timeline for basic keyframing of video effects and individual frame edits; it's certainly no replacement for After Effects CS3 Professional, but will serve in a pinch. Though I can understand the development reasons behind splitting the motion capabilities into a separate package, it's a shame to deny Web or mobile designers the ability to, say, animate the movement of a drop shadow via the Global Light setting, unless they fork over the extra $300 bucks.
Though based on the veteran 10th-generation Photoshop CS3, Photoshop Extended feels like a version 1.0 product tacked on. If you have the budget and want to experiment with the new tools, it's certainly worth a try. But if you're looking for the same streamlined, high-productivity tools for technical analysis, 3D imaging, and video/animation that Photoshop brings to traditional imaging, you'll need to wait a version or two.