From Lewis Carroll's Through the Looking-Glass :

"Well, in our country," said Alice, still panting a little, "you'd generally get to somewhere else — if you run very fast for a long time, as we've been doing."

"A slow sort of country!" said the Queen. "Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!"

Years ago I took an evolutionary psychology class in college, and while most of it stayed in my head just long enough to BS my way through the essay questions, one thing that stuck was the concept of the Red Queen phenomenon in evolutionary sciences.

The general idea is that any advantage a species has ceases to be advantageous once the larger community has access to it. What's more, at some point the unique advantage "tips" into a prerequisite for existence - you have to have it to stay in the race. This typically results in a escalation, with everybody having to run faster and faster just to keep up.

While this dynamic seems to apply anywhere competition exists, it has always seen most prevalent to me in the world of SEO/SEM. Blogging is the easiest example, wherein it used to be an unfair advantage over the competition; it's now a common practice. In most cases its a disadvantage not to have a blog or some means of frequently updating content.

Another issue that is getting more and more prevalent is the rel=“nofollow”. Having built a directory of social media sites to be used in link campaigns, I found that 6 months later, almost half of them had become “no follow”, rendering them worthless for earning link juice (Interestingly, as the sites became mute in terms of passing juice, the click-throughs improved, perhaps as a result of SEOs leaving for more fertile ground?).  

Having been in the field for only a few years, I wonder how accurate this analogy is when applied to the evolution of SEO. Is the development of the field an escalatory process, each day requiring us to run a little faster than the day before? Or is the development of the field more of a moving target, stepping out of one set of practices and entering into a new set, still moving but without the ramping up?

Side Note: This being my first post, I'd love to know if this is the sort of thing worth reading!