Abstract: For better or for worse, XML has emerged as a {\em de facto} standard for data interchange. This consensus is likely to lead to increased demand for technology that allows users to integrate data from a variety of applications, repositories, and partners which are located across the corporate intranet or on the Internet. Nimble Technology has spent two years developing a product to service this market. Originally conceived after decades of person-years of research on data integration, the product is now being deployed at several Fortune-500 beta-customer sites. This abstract reports on the key challenges we faced in the design of our product and highlights some issues we think require more attention from the research community. In particular, we address architectural issues arising from designing a product to support XML as its core representation, choices in the design of the underlying algebra, on-the-fly data cleaning and caching and materialization policies.