Science ran a news article on Grid recently. It's a nice piece. My only criticism is its somewhat narrow focus on high energy physics: certainly understandable given the constraints of a short article, but unfortunate if it gives the impression of a narrow user base. Nothing could be further from the truth. There are certainly hundreds--probably thousands--of Grid projects that span a remarkable range of disciplines and countries. This very breadth makes it hard to get one's head around them all.
Good examples of discipline-oriented projects from fields other than high energy physics include the National Cancer Institute's Cancer Bioinformatics Grid (caBIG), the NSF's Network for Earthquake Engineering Simulation (NEES), DOE's Earth System Grid (ESG), DOE's Fusion Collaboratory, and the French Grid5000 for computer science research. These are collectively delivering value to thousands of users. (ESG alone has 2000 registered users.)
We should also mention infrastructure projects like the U.S. TeraGrid and Open Science Grid, NAREGI in Japan, the UK National Grid Service, APAC in Australia, and the China National Grid, all of which are supporting large multidisciplinary communities.
These projects are all using Globus software, by the way ...