Weekly Play News scored an interview with Shigeru Miyamoto as part of post release coverage for the recently released Super Mario 3D Land. In addition to general questions about Mario Land, the site asked Miyamoto about his current level of involvement in game development.
Miyamoto describes his current work flow as something like "Continually playing the games and checking their content, and sharing my opinion with the development staff." He usually does this for about seven games simultaneously, although he'll really focus on around three games per year.
The development staff at Nintendo all work on one floor, explained Miyamoto. When sharing his opinion on a game, He'll write his opinions in a checklist form and show this to the game's director as they speak. He takes care to clearly explain his directions and the reasoning behind them.
Miyamoto will spend a good amount of time playing games. On game heavy days, he'll play for around 10 hours a day. During the final stages of Zelda: Skyward Sword, he was pretty much playing the game whenever he wasn't in a meeting.
Turning to Super Mario 3D Land, Miyamoto said that development took around two years. The initial development started with just two people, but in the end, they had 30 people working on the game. Miyamoto describes Mario Land's development as having a good pace.