Buy versus build is a discussion that comes up a lot in the IT and management field, especially if you are a consulting firm like Allegro. The problem with "buy" is that it is never that easy. The question should really be "integrate versus invent" as no matter how cookie cutter your new IT application, it will have to be connected with the rest of your IT infrastructure to truly be of any value to your business.
This article from InformationWeek looks at the hidden impact in losing technical expertise for companies that too blindly pursue an "always buy" mentality. While you do not want to painfully build everything yourself, you will need that expertise to skillfully integrate any bought IT system with the rest of your business infrastructure and then extend it to reflect and enhance the unique benefits that your company offers over your competitors.
This is why we at Allegro have turned to open source applications such as the world leading Magento eCommerce platform. Your "buy" choice can start with a baseline Magento installation that has all the core eCommerce functionality necessary. Supplement that with the "build" addition of targeted modules and custom enhancements and integration, whether from your internal staff or quality consulting firms such as Allegro. This type of strong integration and customization is where companies really stand out.