Using the Grid Infrastructures provided by EGEE, OSG and others, a worldwide production service has been built that provides the computing and storage needs for the 4 main physics collaborations at CERN's Large Hadron Collider (LHC). The large number of users, their geographical distribution and the very high service availability requirements make this experience of Grid usage worth studying for the sake of a solid and scalable future operation. This service must cater for the needs of thousands of physicists in hundreds of institutes in tens of countries. A 24x7 service with availability of up to 99% is required with major service responsibilities at each of some ten "Tier1" and of the order of one hundred "Tier2" sites. Such a service - which has been operating for some 2 years and will be required for at least an additional decade - has required significant manpower and resource investments from all concerned and is considered a major achievement in the field of Grid computing. We describe the main lessons learned in offering a production service across heterogeneous Grids as well as the requirements for long-term operation and sustainability
