From a personal point of view, I'm convinced you have to enjoy going to the place you work in. Improving your day to day experience feels revolutionary enough for me.
I also think design and usability can improve not only the way a company thinks about new products and customers think about the company, but also how the company sees itself internally. I work in software development, and we usually talk about innovation, atmosphere, team building and all that.
I'm trying to think what I can do, as a designer, to make internal communications more fluent and fun. I'm struggling with the actual ideas. For example, graphs are great, they can show survey results and motivate people to improve... newsletters are fine, nobody really reads them but they are something. Magazine-like publications are good too. And that's as far as I've come.
Can you think of any other ways design can help internal communications?