Since most programs can be broken down into a set of components I believe it should be relatively easy to parallellize the workload.
The "easy" part of your phrase, is the one key misconception that project managers have since the beginning of software engineering. The mythical man-month and peopleware anyone?
While I think the individual parts could be considered easy, the interaction of these and their integration I would consider a hard, complex problem with the potential to bottleneck all of the work.
The reason being: it's very difficult to parallelize integrative work because by its very nature, functionally it suggests dependency and coupling, and socially requires efficient communication.