The team at MTD is extremely knowledgeable in their field which makes working together seamless! I have not had any issues thus far but when we do it's typically our fault for underestimating how much work would be involved or overestimation of what could actually happen during setup/implementation.
Our client has been very happy so far - they've done some interesting things like using geolocation tools (Google Maps API) as well as implementing custom dashboards that show them key metrics about each call flow within their system via Salesforce Analytics.