Digital Web Magazine have an interesting article on packaging design for web-based products, by Luke Wroblewski. The article introduces Packaging Design and the different issues related where designers Differentiate, Attract and Embody the Brand. An excellent usability and branding experience mixed together to create the right package.
Packaging Design

Though hundreds of years of packaging design history and best practices may have influenced your offline shopping behaviors and decisions, the lessons learned in this enduring discipline didn