Visio 2013 introduces a new OpenXML based VSDX format which offers great new possibilities for developers. Combined with the native rendering on SharePoint 2013 and Office 365 there is a whole new world of solution opportunities available.
Here's a post with tips and tricks for developers on the new Visio blog.
http://blogs.office.com/b/visio/archive/2013/01/29/10-tips-for-developers-working-with-the-visio-vsdx-file-format.aspx