Blacklaw writes with an article in Thinq about the upcoming quad-core Tegra chipset. Quoting the article: "Nvidia has released a few technical details of its upcoming 'Kal-El' Tegra processor, including a secret it's done well to keep under its hat thus far: it's a five-core, not four-core, chip."
The fifth core will be clocked lower and is intended to let the system use little power without having to fully suspend. A few years ago Openmoko had a vaguely similar idea to include a microcontroller for low-resource idle tasks (e.g. GPS logging), but this design is superior since it should be more or less transparent to user space programs.