Dyer points out that offline self-identification is contextualized, oral, and voluntary.
Online identification, on the other hand, is decontextualized, text-based, and declared prior to anyone's asking for it.
Clearly there's something to this. But I would argue the lines between online and offline identity are not quite as distinct as Dyer makes them. His distinction serves as a helpful heuristic device, but involuntary disclosure is a feature of our offline lives inasmuch as it is a feature of Facebook.
Granted, such disclosures may not be as substantial or important as those that we disclose personally. But they do occur.
I wore a rosary bracelet for a few months as an experiment, and people automatically--and falsely--identified me as Catholic. I would wear a suit to church events and people would automatically assume I was either a lawyer or in finance.
These identifications aren't always benign, as in the above examples (see: racism). But they're not inherently problematic, either. Rather, they expose the fact that the meaning of our the various possibilities of our identities precedes the fact that we choose to identify ourselves in certain ways. Trying to limit people's perspectives of us to only what we consciously disclose about ourselves (if possible) is simply too narrow.
But then, that highlights the shortcomings of Dyer's understanding of how we identify ourselves online. While we might be limited to text on Facebook (profile pictures?), that is certainly not the case anywhere else on the web.
As a case study, look at Mere-O. The first things that grab people are that we like old, strong stuff. And that we have a very old looking site (yes, it needs to be changed). Design is precisely that which contextualizes the words that bloggers write, and provides additional layers of meaning to it. At least when it's done well, which we haven't done for several years now.
That said, Dyer's categories are enormously helpful. But reality resists such careful categorization and dichotomies, even while they open up avenues for new reflections and thoughts.
Matthew Lee Anderson is the Founder and Lead Writer of Mere Orthodoxy. He is the author of Earthen Vessels: Why Our Bodies Matter to our Faith and The End of Our Exploring: A Book about Questioning and the Confidence of Faith. Follow him on Twitter or on Facebook.