What makes a value proposition compelling is same as it ever was in marketing. Web or no Web.
We still live in a multi-channel world. Now there is empirical data showing that most word-of-mouth marketing happens off-line, not online. Check out the findings of the Keller Fay Group, which said that 90% of the of the conversations people have about products, companies and brands do not occur on the Web.
This should be a wake up call for marketers obsessed with social media. It suprises no one who has understood that a toolbox is not a strategy and that marketing techniques and tactics have always been in a state of evolution. Look at it this way: Autodesk tools changed the way architects practice. But the principles of architecture, structural engineering, materials science and mathematics are the same for the construction of the new Bay Bridge as they were for the Egyptian pyramids. The way we reach out to markets today are a far cry from yesteryear, but the things that make a product’s value proposition relevant and compelling to a buyer are the same as they ever were. The same in the age of Zuckerberg as they were in the time of Gutenberg, and long before that. Knowledge of your customers trumps knowledge of whatever tool you happen to use to reach them. Indeed, the former will always determine the latter.