I thought about cooking up an actual formula, like F=MA (force = mass X acceleration, the only thing I remember from physics), but I'll pass for now. Formula for what you ask? Well, it's like this.
Social media content (comments, links, photos, etc) is constantly moving. Now, I don't just mean the act of being passed from person to person (Facebook = Share This / Twitter = Retweet). This isn't about the viral nature of social media so much as it is about the way stuff we post 'moves' across a person's field of vision. Stay with me.
Say you post a message on your personal or business Facebook Wall ('what's on your mind'). It not only appears on your Wall, but more importantly, is pushed to the News Feed of everyone you're 'friends' with, or everyone who's a 'fan' of your Page. Now, the news on all of those News Feeds moves at different speeds. When you glance at your personal News Feed, you notice content - from people and businesses - moves downstream, in conveyor belt fashion. As new content appears, older content slowly (or quickly) moves further from your field of vision. This, in a nutshell, is the 'velocity of social media', and it's directly relative to the number of connections a person has. If someone has 600 Facebook friends and is a fan of 85 Pages, new messages might appear every minute or two (experiencial guess). If someone has 85 friends and is a fan of 15 Pages, content will stick in their field of vision for a longer period of time.
Why does this matter? Well, if you're a business operating a Fan Page, then you need to put yourself in the social media shoes of fans, understanding the way content - and those that share it - behaves. Your message might be noticed, initially, by a only a modest percentage of your total fan count. If your content is interesting, then it may be shared again by some of that initial group (which is a main goal in social media).
The factors that determine how many people see your message in their News Feeds include velocity, time of day/day of week the content is shared, how often you communicate, and random 'X' factors such as 'frequency' (how often a person checks Facebook), 'curiosity' (some love to know what people and businesses are saying, others could care less) and 'quality'. I can't emphasize quality enough, since that's something you can control. If you consistently post so-so stuff, Fans will start to treat your content like junk mail. Content is still king, but you also need to start understanding the dynamics of how content moves now ... so your content has a decent shot at being consumed, shared, and responded to.
I want to explore this concept more ... the way content moves ... in the comment section of this post (your comments are coveted!), and in additional posts. Twitter is another monster, deserving of its own post, since content there can move in the blink of an eye. It's not as simple as a business having a formula that says "the number of friends a person has, combined with the number of Pages he/she is a fan of, Plus the average number of times that person checks his/her Facebook News Feed each day/hour = the Velocity of social media ... and therefore you should do X,Y,Z". It's not about a mathematical silver bullet. What I'm trying to say is yes, numbers matter. Coke, with 5 million Facebook Fans, can reach out and touch tens ... hundreds of thousands, with one simple post. But since the key word in social media is 'social', each of those 'numbers' is a person ... each matters, each behaves differently, and each is a potential brand ambassador. Treat them equally fantastic, because you never know who might have an impact on your business (positive or negative).