Engadget had an interview with Bill Gates at CES 2008:
One last question: what kinds of pet technology products do you think you'll be keeping at Microsoft? You've got to have your fingers in the pie a little bit!
I love natural user interface and particularly the research groups to do that. I want to stay involved with that and make sure that when it's time to really put these things in the mainstream that Microsoft is jumping on it and taking that big risk. Search is obviously a huge thing for us that we put about a brilliant people on. Right now -- people don't know -- can do something really differentiated that could be fun to help drive that piece forward? Steve [Ballmer] will pick; my non-Microsoft time I'll be thinking about software for health systems and education. So I will probably be over at Microsoft seeing where their breakthroughs can help in those areas. But the day of the week that I'll be at Microsoft will be probably three projects, I'd guess.