It seems that Intel's private goals for their heavily-invested-in Ultrabooks have leaked out, where they hope to have between 20 and 30 million units sold before the end of 2012. The supposed internal roadmap details were passed onto DigiTimes, and those numbers are said to either double or triple in 2013.
By 2013, the supply chain would be truly ready for mainstream adoption, with reinforced plastic available to emulate to rigidity of metal without the higher cost. The next wave of Ultrabooks are nearly upon us as it is, with Ivy Bridge-based Ultrabooks nearly ready. Touchscreen-based Ultrabooks will arrive with Windows 8, which is when sales should begin their very large vertical climb in numbers.
Early sluggish adoption of Ultrabooks has been blamed on Windows PC builders not being used to developing with the higher-end components that Apple are used to. These include aluminum, solid-state drives, and low-voltage Core i5 and i7 chips. This should change as time goes on, and the higher adoption rates of not only Ultrabooks, but the components within them.
Windows 8-based Ultrabooks can't come soon enough!