The Visio 2007 Viewer Developer Reference is up on MSDN and can be accessed at: http://msdn.microsoft.com/en-us/library/cc297217.aspx.
The reference includes the full API reference and some short samples on how to embedded the viewer in different environments. The Viewer provides an application programming interface (API) that enables solution developers to perform the following tasks:
Please please please please include Visio 14 in at least some Office 14 SKU, at least Enterprise and Ultimate. I don't need InfoPath as a non-enterprise user, I need Visio.