The idea is to avoid moving your hand from the keyboard to a mouse over and over again. At first sight this looks a bit weird, but according to engadget, it really works.
However, this is not going to work unless one knows touch typing. There are number of programs that do teach touch typing. link.
Myopic view of technology, computer
Update - November 2013.
Looks like there has been some traction. The team behind combimouse also have been looking at crowdsourcing - http://www.indiegogo.com/projects/combimouse-combination-keyboard-and-mouse--43 and as per their project plan intend to complete the full mechanical design and finalize the prototype by December 2013.