I've been very heavy on the idea that the fact that something is popular doesn't necessarily mean that it's valuable. Sometimes it is, but value is a property of meaning, not a property of popularity. Given that popularity is a property of accessibility, it's easy to make a case for the above: accessibility is directly opposed to scarcity, which is a key measure of an important kind of value.
Here are two more ways to look at this:

1) For the visual types:

2) For the logical types:
popular = accessible
accessible = ~scarce
scare = valuable
∴ popular != valuable

An important related implication of the above is that something being profitable doesn't necessarily mean it is valuable, either. In an excerpt from the post "Payola," Seth captures these ideas below:

The New York Times bestseller list is even more easily manipulated than Billboard ever was. It doesn't cost much to scam it and it's pretty straightforward to buy your way onto the list (I know authors who have done this and consultants who sell this service.) You can hire a bunch of old ladies who will go into the 'right' stores and buy books on the right day. As a result of this distortion, the books on the list get more promoted, and thus sell more copies. It's not pretty but it's true.
via sethgodin.typepad.com

Certainly, there is in fact a kind of value that both popularity and profitability can measure. I see these as indicators of something being what I call "business-valuable," and I include them on the right side of what I'm calling a paradox in the image above.  

From Seth's excerpt above I can't help but be reminded about SEO and any number of other strategies that I generally think of as "putting business-valuable before wisdom/long-term valuable." It's easy to look at the first and notice that it is in fact a kind of value, without considering the other (I argue more important) kinds of value in the world.