At Thoughtworks, as early adopters and leaders in the agile space, we've been proponents of the practice of incremental delivery. We've also advised many clients to look at off-the-shelf software through a "Can this be released incrementally?" lens. This has often been difficult because of the big-bang approach of most vendors which usually involves migrating large amounts of data. Recently, however, we've also had success using incremental delivery with COTS (commercial off-the-shelf), launching specific business processes incrementally to smaller subsets of users. We recommend you assess whether you can apply this practice to the vendor software of your choice, to help reduce the risks involved in big-bang deliveries.