Mario Gudelj and Eddy Chan (Two Blokes With A Postie) have teamed up to offer a Business Catalyst - Zendesk Integration service to the Partner Community. They've built a web service that can pull cases and contacts from BC and push them as 'tickets' and 'requesters' into your Zendesk account. It can also grab new 'requesters' from your Zendesk account and sync them back to the BC CRM so you can use email marketing to contact them.
What does this mean for you as a BC partner? It's a new service that you can use yourself or offer your clients, especially the bigger ones where there is a team of sales staff or customer support staff who need to use a dedicated customer service app like Zendesk but at the same time need a custom designed BC site to generate leads or field support queries via webforms.
All they need to do is create an account on their integration server with the details of the BC site and Zendesk account to be synced, then customize the app to setup and match your BC form fields with Zendesks custom ticket fields. Integration of one BC site to one Zendesk account starts from AU$995, you can read more about it at their blog. Be sure to ask about their custom API dev services too, they can connect BCs API to anything with a SOAP or REST API to add that extra functionality your client needs.