BizTalk Server has seen tremendous growth since the groundbreaking 2004 release. Customers and partners alike have implemented many mission-critical and highly complex solutions based on the BizTalk platform, bringing Microsoft technology to the heart of organizations (which was largely unheard of before).
The BizTalk Server platform is incredibly powerful and arguably complex; much of this is not necessarily because of the product but because of the problem spaces that it typically occupies. I've yet to come across a straightforward set of requirements for a BizTalk solution. It is used as the central backbone of huge organizations, the integrator between disparate and complex applications, and the platform for entire financial trading platforms, and the list goes on.
Such scenarios are incredibly complex; they demand high and sustained message rates, can tolerate no downtime or data loss, and are often central to an organization's operation. If the solution were to fail, an organization could lose significant amounts of money or incur regulatory penalties.
I like to borrow a well-known tag line to describe BizTalk in situations such as this, "with great power, comes great responsibility." BizTalk Server is incredibly powerful and can be applied to solve many scenarios. To do so, however, you have to architect, develop, test, and administer such a solution responsibly.
Any compromises in these stages can lead to any number of problems: the solution might not scale, it ...