Salsa Engage provides a robust interface to Salesforce--our primary CRM--allowing non-intervention synchronization to categorize supporters into groups for email communication. As we are only six months into our implementation, we have not found areas where it's not appropriate to use beyond nit-picky synchronization delays and smart group updates.
It works okay if you have a large budget and don't have the technical experience on your staff to set up NSPS appropriately. It probably also works better as a purely development-driven database; trying to track multiple departments with very different goals in the same database is challenging.
Support response has been swift and knowledgable, though not always the answer I've wanted. One huge design flaw is if I add a new Salesforce field to sync, Salsa Engage will not sync it unless it has changed since the last sync, requiring me to fake an update for an entire database or re-sync the whole enchilada. Better to recognize it's a new Salesforce field and perform the sync en masse.
Support for the product is horrible; often support will have you bouncing between Blackbaud support and Salesforce support and it's very rare either are able to find simple solutions. Most of the time the solutions almost always cost money and hiring consultants which, for a smaller organization, means not being able to achieve proper solutions.
Salsa Engage is one of the easier products to set up and use, but with that comes limitations. If you want something simple, this works, but if you have more complex needs, then you'd be better off investing in another system that requires more set up work, but provides more customization and robust reporting opportunities.
I recently started using EveryAction, it is much more robust and nimble and does not need a lot of customization. The only big feature I miss is the acknowledgment process for Luminate CRM and Analytics: it was much more robust, but overall it doesn't have the cumbersomeness of Luminate CRM. I don't think I would ever switch back.