Salesforce has for years made an effort to make it easy for other applications to connect with their system. They even help vendors sell their certified add-on applications via the AppExchange. The web service API for Salesforce.com is often used to build integrations between Salesforce.com and other systems, for example to integrate with ERP systems such as Microsoft Dynamics, e-conomic, etc. If you are considering to use the API access for salesforce.com to build your own, custom-made Salesforce-ERP integration, maybe with the help of your partner? Have you also considered a data integration platform?