And of course the inevitable query about what it is he'll be doing exactly in his new, expanded role at Microsoft popped up. Here's what the former Microsoft chairman had to say:
"I am excited about how the cloud and new devices can help us communicate and collaborate in new ways," Gates wrote. "The OS won't just be on one device and the information won't just be files - it will be your history including being able to review memories of things like kids growing up.
"I was thrilled Satya [Nadella] asked me to pitch in to make sure Microsoft is ambitious with its innovation. Even in Office there is a lot more that can be done."
He later added: "I make sure we pick ambitions scenarios and that we have a strong architecture to deliver on them. I encourage good work (hopefully)."
When Nadella was named Microsoft's new CEO last week, Gates said he would devote over a third of his time to product groups. He also mentioned working with the product team during today's AMA, and his comments about the cloud and devices speak to Microsoft's new "mobile-first, cloud-first" mantra.
Nadella has already talked up the Internet of Things, how devices are driven by software and Microsoft's ability to lead in both; from his comments on Reddit, Gates seems on board with developing products and services for a more connected world.
He even spoke about machine learning when quizzed what he would study if he was a current computer science student:
"The ultimate is computers that learn," he wrote. "So called deep learning which started at Microsoft and is now being used by many researchers looks like a real advance that may finally learn. It has already made a big difference in video and audio recognition - more progress in the last three years than ever before."
Smarter machines may be in our future, but Gates is firmly stuck in performing at least one old fashioned chore:
"I do the dishes every night - other people volunteer but I like the way I do it."
- Gates also said he's digging his Surface Pro 2 - perhaps you will too after reading our review!