The Dell XPS Duo 12 mounts its fold-over display in a frame. The panel rotates in the frame, allowing the display to fold flat over the keyboard. The IdeaPad Yoga, meanwhile, has a display with a friction hinge that allows users to orient the panel at any angle: You can open the lid by 90 degrees and use the panel in laptop mode, or you can fold it a full 180 degrees and run the device in tablet mode, at which point the exposed keyboard deactivates.
These convertible fold-over systems are more like laptops than tablets. Indeed, IDC's Mainelli notes that IDC categorizes convertibles as notebook PCs, but classifies devices with fully detachable screens as tablets.
The latest hybrid devices are sleeker and offer better performance than the Tablet PCs of yore, but they fare poorly when matched against today's standard high-performance laptops, and even against Ultrabooks, which make their own compromises in the service of ultraportability. Though some hybrids will offer Ultrabook-caliber CPUs, memory, and storage, their screens will be smaller, at 10 or 12 inches instead of 13 or 14 inches.
Worse, detachable slate hybrids have docking mechanisms that introduce a potential mechanical point of failure. And because they include batteries in both the keyboard dock and the main system chassis, slate hybrids are bulkier than the new crop of extremely thin Ultrabooks.
Fold-over hybrids more closely resemble laptops; and in the long run, they may not present as many consumer caveats. Lenovo's Yoga easily satisfies the Ultrabook spec and carries a 13.1-inch, 1600-by-900-pixel display. The hinge design may be worrisome, but it's probably less problematic over the long haul than a detachable dock.
Caveats notwithstanding, you may still be committed to dipping your toe in hybrid waters. If so, you have to decide which of the two basic designs makes more sense for your needs. The short answer: Get a fold-over convertible if you're interested in serious productivity, and get a detachable slate--or even a pure tablet like the Microsoft Surface--if you envision a more touch-focused life ahead.