Changes are afoot at Twitter, still in search of a business. Now it is trying to see if changing/switching management will help: Evan Williams and Jack Dorsey are switching roles at the company, with Williams moving from chairman of the board to CEO and Dorsey relinquishing the CEO post to become chairman. In a blog post, Williams said his enthusiasm for the company has grown even stronger and that it’s a “huge potential” that “deserves my full efforts.” Williams gives Dorsey credit for originally coming up with the Twitter concept and praises him for leading the company through two rounds of financing and building its team. Like so many startups, Twitter still suffers from, well, lack of a business model. And while $15 million latest round helps it buy some time, and it’s been working on integrating better tools and services, it has watched a few competitors crop up with similar services at a good clip, including FriendFeed and others.