With ‘OK’ button, ‘Cancel’ should appear as secondary button or link?

When I make web application designs, every time I style form or overlay boxes with OK and Cancel buttons. I think of making them different. But is it a good practice?

Some people recommend primary and secondary buttons, but I don't feel 'cancel' is so important to give it a secondary button status. What if the application doesn't have enough secondary buttons? I don't want to create and use a secondary button only for 'Cancel'.