Microsoft seems to have just discovered these however they have been around for years.
Ultra books are basically really thin laptops which can perform as well as an expensive computer. Apples MacBook Pro is a really good example of an Ultra-book because it is really thin and lightweight yet still has a brilliant processor, internal memory and graphics.
The only problem with ultra-books is the massive price tag that they have (usually between £1000 - £2500) and for that money you could get something a lot better than an ultra-book. A decent second hand car perhaps or a holiday somewhere warm like Spain?
It is understandable that because they are new they have a hefty price tag so we can only wait in hope that the price decreases.