Paired Programming is always brought up and usually discussed in any discussion of agile development. I worked on a project where we did pair programming. I considered it successful, but my recent attendance at the Better Software Conference sparked the following idea.
Paired Development with a programmer and a tester(QA). Logistics aside for the moment, a programmer writes the code sitting with a tester writing the tests for that code. They would decide on the design of the task (dependent upon the project constraints and procedures), and I would imagine they would review each others work. I believe review is the important concept in paired programming. I would think a trained tester would be more capable of writing unit tests then the programmer, since I find that the processes are complimentary and difficult to switch between.
This concept would need more thought, however if good processes are used and roles are defined properly, I think this might have some promise.
Allen