Ubuntu Netbook Remix is their optimized Ubuntu environment designed specifically for Mobile Internet Devices (MIDs) and Ultra Mobile PCs (UMPCs). Netbook Remix is optimized for devices with Intel Atom processors and leverages Intel's Moblin project.
Compared to a full-blown Ubuntu installation, the Netbook Remix will be offered by OEMs and will feature a stripped-down version of this Linux desktop distribution that's enhanced for web connectivity and mobility. While Netbook Remix is being shown off at Computex, sadly it won't be available to consumers until later this year.
More information in the Canonical press release.