The latest releases of S4S (1.80.16221.4, 1.81.16230.1, and earlier) have a number of fixes that address volume processing and MVC support.

S4S talking to multiple Salesforce instances

S4S was caching the KeyPrefix to ObjectType mappings which created challenges when switching from one Salesforce instance to another. The fix added the Salesforce OrgId to the cache key to prevent future conflicts for custom object key prefixes. A new method ClearKeyPrefixCache() was added to allow the KeyPrefix Cache to be cleared.

Web Forms For Marketers

A fix was made to S4S Mapping Wizard due to the way Sitecore has changed the contents of the AdaptedResultList used in Save Actions for MVC forms. The S4S PushVisitorAction Save Action now uses the identity of the item field rather than the underlying item name.

Another change to the item tree allows customers that create their own Save Actions to see the action in the S4S Mapping Wizard. This particular fix is a breaking change as it adds items to the Sitecore content tree. 

Sitecore Analytics in Salesforce

A significant performance fix was made to the BulkUpdateAnalytics scheduler so it now updates Salesforce with fewer API calls.