When you first launch the application, you are able to set the default vCard to send. When you navigate back to the vCard tab, and tap the "Send Card" button, you will have the option to send the card via email. In the email section, you can either type in a new email address, or select an email address from your contacts.
This application does make sending card very easy, but for the price I would like to see more functionality. For instance, it would be nice to send one card to multiple people. Also, the vCards are delivered through the developer's mail servers (which is a do-not-reply account) -- I would like the email to be sent from the default mail account on my iPhone, as the recipient would be more aware of who the card is from. However, as it is, the application is very useful, and just plain works. You can download Sharecard from the iTunes App Store for $1.99US.