An interesting article that puts forward some good reasons why you may not want to use third-party assemblies. This is probably very relevant to the software being developed in this case but the rule stated, "no third-party assemblies were allowed" is a little too wide-ranging.

A good example would be where in recent projects we have used the Infragistics controls for Windows. These have speeded up development of commerical bespoke developments and produced software with a user interface that would not have been possible to achieve within the customer's budget without using externally developed components. However, the interfaces for Infragistics are so complex that it has made the learning process for the controls be a long one. This validates one of the articles points though I think the overall effect of using the third party components has been positive.

Hmm.. I agree. We're creating a large(ish) desktop application using two major third party controls. Creating these from scratch ourselves simply would not have been feasible.

Once we are well estabilshed we may rewrite - but it isn't a high priority.