I was told there would be no math. 

Contrary to the title of this post, this is not about math per se.  It is about a way to think about how a product is consumed and advocated by your customers.  For the math on this, check out this post from Robert Zubek.

Essentially this is a measure of how "viral" your product is by measuring how many additional users you acquire from each subsequent user.  You have done very little to acquire these customers other than create a great experience for the initial user and have a great product.  Get it?

On-demand/SaaS delivery models allow people to access products and information about those products and the problems they solve at will with a browser and internet connection. 

You can build product functionality to facilitate this with "share this" or "refer a friend" capabilities and, of course, ask your customers to bring you new customers as 'word of mouth' is the holy grail in a modern marketing plan.  It is hard to create this artificially but is amazing to watch when it happens organically.  One of the companies I am working with is seeing this happen and it is really fascinating to watch.

I also like this post by Josh Kopelman on what to do "After the TechCrunch Bump."  The herd that follows posts on sites like this are not target users finding value in your product that they want to share with others.  They are more akin to wildebeests following the lead animal across the plains of the Serengeti making a huge amount of noise, gone before they got there, and leaving behind a great deal of destruction and waste.