Positive feedback on data entry

The registration form at Myfico.com provides users with positive feedback ("Thank you") after they correctly complete each field:

Mint.com also uses this approach with their login form, though the feedback is a more subtle "OK" to the right of the field:

This may seem like overkill, but I can see how users would respond favorably to knowing they've completed fields correctly. That way they can submit confidently—without the fear of having the form returned with errors.