Life is short. No one wants to fill out a form. Be conversational. Be funny. Gradually engage. Do the unexpected. It is the role of the designer to express their company’s brand to elicit an emotional reaction.
If done correctly, it will increase completion rates. Just make sure you don’t violate the rules listed above.
When thinking of User Experience, we often think of a simple, beautiful, and easy to use feature-set of a product, that makes the user’s life easier. But as a matter of fact, features are merely a small, fragile part of the product.