For most of the 20th century, professional designers had a clear project in view. Modernism was the order of the day, and functionality, simplicity and innovation were unquestioned virtues. Today things are messier. We have become more aware that different people around the globe want and need different things. Style cults come and go so quickly that keeping track of them is an industry in its own right. Progress itself is coming to seem a dubious prospect, given contemporary debates about the environment and the increased appreciation of traditional culture. These days who is to say what constitutes good design? Glenn Adamson enjoys a rapid-fire and illuminating ode to contemporary design