The incorporation of grain into an image is no different then the use of different brush techniques or texture of the paint when applied using oils and acrylics.
Grain is just another tool of expression available to the photographer and is often maligned by the F64/ Ansel Adams crowd. But it is one of those characteristics that is unique to the medium and the the right hands produces stunning results. Ralph Gibson is the true master of grain, using the classic combo of Rodinal and TriX for his images from the 70s-early 90s.
Bill Brandt, (one of my favorites) used grain to great effect and a great number of Robert Frank's images from the Americans have significant grain. And also as Jorge mentioned Eddie Ephramus and Les both use grain in many images to produce beautiful work.
By the way, any idea why grain seems to be a much more prevalent tool in the UK and Europe?