The M.A.C. Pro Team of makeup artists—fixtures backstage at more than 175 fashion shows worldwide—are using Twitter’s micro-blogging service to give real-time updates about their experiences working behind the scenes at New York, London, Milan and Paris fashion shows this fall. With Twitter—a service in which people “tweet” each other on their computer or phone through quick, frequent exchanges limited to 140 characters—fashionistas and makeup lovers were able to reach M.A.C. senior artists in r...