It seems the rumours were right - nVidia does indeed have an Intel Atom platform. It's called Ion, it's crazy small enough that it should fit not only into nettop systems, but also netbooks and, importantly, should offer much better graphics performance than Intel's 945G platform.
Based around the same 9400M chipset powering the new Macbooks, but on a pico-ITX motherboard. Ion refers to the combination of that chipset and Intel's Atom processor.
Looking at the reference design, it's clear just how small nVidia's platform is. In fact, the board is small enough that not all of the component points fit on one side - so the RAM SO DIMM slot and a single SATA connector are on the reverse to the chipset and CPU. While not superficially the best looking system in the world - those front ports should really be covered - the sample machine really goes to show just how much can be crammed into a small space using 9400M. It's a good indicator of what OEMs will be able to accomplish with systems that are actually made available to buy - which nVidia's wont.
A crazy six USB ports, optical digital and analogue audio connectors, and a pair of e-SATA ports at the front alongside VGA, DVI and HDMI outputs, a further USB port and an Ethernet jack at the back blow all current Intel-based solutions out of the water on the connectivity front.
There there's 9400M's ability to decode up to 25Mbps HD video and output 8 channel (7.1 surround) Linear PCM audio over HDMI. Throw in nVidia's claim that Ion should offer the same battery life as Intel's netbook platform, but taking up half the size and the green team should really be on to a winner!
Over in the US AnandTech managed to get hands on with an nVidia reference sample and were, not unsurprisingly, impressed. I suggest heading over there for more details.
Hopefully I can get my hands on one of these things myself soon - if it packs a dual core Atom, so much the better.