I have been researching the vCard format recently. I am planning to add this as an output format for the Email Sign Up app because the Android contact manager can import vCard files. This will allow users of Email Sign Up to import their collected email addresses directly into their device’s contact manager.
The vCard for Developers was one of the most helpful links.
These vCard notes were also helpful.
There is a Java library for reading and writing vCards that was extracted from the Android source code.
Finally, the actual RFC vCard file format specification.