Twitter on business cards is mostly as a form of connection (same as an email address). For many people it's a dumb idea, but in some circles (a good example being tech marketing) it can be useful. If someone who actively uses twitter follows you, and you're an active user too, it's a constant reminder that they know you, and they won't forget who you are.
In the example you gave (and it was a very good one, it makes sense), wouldn't it be more prudent to link to a github profile or something otherwise reduces the layers necessary to obtain access to what makes you relevant to the viewer's interests?
