Since Sitecore introduced its Connect for Salesforce CRM connector, we have been asked to explain the differences between it and S4S.
Briefly, they have very different approaches to data integration to your business needs, network infrastructure, transaction volumes, data recency and support requirements all factor into your decision. At FuseIT we see S4S as the enterprise solution, already fully proven by very large customers and tested with large data volumes. Technically the products are fundamentally different, S4S transacting data in real time while Sitecore Connect replicates data using synchronization processes. S4S has many OOTB features that quickly get new customers up and running whereas Sitecore Connect requires more developer input to create and configure the required functionality.
A full comparison chart is available at http://www.fuseit.com/products/sitecore-salesforce-integration/s4s-vs-sitecore-connect/. To learn more about how S4S can add value to your business please contact us for more information.