More of a minor observation than anything, but... thinking back to "Interface," it struck me that there's a common theme between this book, The Big U and Snow Crash. Specifically, each deals in some way with the idea of the bicameral mind. Taken in this light, you can see a really fascinating evolution as Stephenson's career progresses; it's like he got this idea, sort of played around with it at first, then used it more seriously and explicitly, then finally made it a crucial cornerstone for one of his best books.
The rest of this post briefly discusses some aspects of all three books. Some plot points are mentioned, and you may want to avoid this post if you prefer going into books totally blind (and know you want to read these books).
As I understand from Stephenson's own words and my spotty research online, some anthropologists and psychologists believe that at one point in our evolution, our left and right brain hemispheres were not as strongly linked. Our ancestors had the same basic physical hardware, with different sectors of the brain responsible for motor movements, memory, language, etc.; however, one sector of our brain was responsible for generating thoughts, and another sector was responsible for interpreting and acting on these thoughts. In modern days, this exchange is seamless, but earlier in history, there was a jump between these areas; as a result, it would sometimes feel like voices were speaking inside one's mind when these thoughts were generated. This, some researchers believe, accounts for individuals believing that God or spirits were directly communicating with them.
In Interface, this sort of division is recognized in Cozzano's recuperation. Basically, his chip is implanted in his interpretive hemisphere (I believe in the left). Therefore, all of his thoughts and actions must pass through here, and the chip thus controls what he says and does. What Mary Catherine does is find a way for his pristine thought-generating center to communicate without passing through the interpretive center. This takes so long in the book because humans no longer use these channels independently; she is essentially de-evolving him to his bicameral state (note how he is consciously unaware of what his left hand is doing).
In The Big U, I believe Septimus Severus actually delivers a lecture on the bicameral mind. It plays a huge role in this novel, but unlike in Interface, it is largely sinister. (No pun intended.) All of the "bad" students have devolved into a bicameral mindset; some do so through the aid of powerful drugs (I forget the former boyfriend's name, if you've read it you know who I mean); others through sheer force of willful ignorance. When you read the book it seems almost spiritual, as though the Go Big Red Fan has been inhabited by a demon who orchestrates the "terrorists" in their actions; on subsequent read-throughs, though, I'm convinced we're supposed to believe that these voices are just that, voices from within their own minds. Their herd/tribal organization means that these students rely on just a few charismatic "listeners" to show them the way, and the rest follow suit. (That is, not all of the "terrorists" have bicameral minds. Their crazy leaders do, the rest of them are just following peer pressure.) Virgil, Casmir, Sarah and the others are most admirable in the ways that they resist their impulses and use critical thinking to guide them instead of the shouted commands from their right lobes. Fred Fine is tragic not necessarily in the way he dies (which is quite heroic), but in the way his mind is broken and he becomes a vessel for SHEKONDAR. (If you like, you can imagine this breakdown as a good thing - that the Fred Fines were able to find wisdom in themselves that would have been blocked in a normal mind - but as entertaining as their lives become, I doubt any of us would want to trade places with them.)
In Snow Crash, of course, the bicameral mind is the main plot point. Unlike Interface, where it was recovered to circumvent an injury, and The Big U, where it was a disturbing devolution, in Snow Crash it is a residual part of the brain that is reactivated by malevolent forces. It is a wetware hack, a way of reprogramming the brain. Stephenson traces this from the mind hackers of ancient Sumeria, describes its defeat at the hands of Enki (sp?) and the origin of Babel; and its resurgence in charismatic Christianity and the future threat of targeted nam-shubs. The bicameral mind is something neat, sort of like a cool security vulnerability: you are impressed by its potential, but know that ultimately it must be shut down. This novel contains Stephenson's most exhaustive (and, arguably, most entertaining) treatment of this topic, and will be considered by many to be the fictional last word on the subject.
Once I thought about this, I realized that this is kind of similar to what Stephenson has done in his later book. This time, the topic is money rather than the bicameral mind. It's the same sort of pattern, where in Cryptonomicon he first started playing around with the idea of currency, its functions and its purposes, its elastic qualities. He didn't really do that much with it, just sort of had people thinking about and tinkering with it. Then, when he gets to Quicksilver, he is prepared to launch a much more in-depth examination of the actual origin of money and how our modern financial systems developed. Money becomes an integral part of the plot merely than scenery, and in his genius he actually makes the topic a lot of fun.
So, that's it. I should mention that I actually haven't read "Zodiac", the book Stephenson wrote between "The Big U" and "Snow Crash"; I want to, I've just been saving it since I'll feel depressed once I've read everything by him and there's no Stephenson left. Anyways, I'll be curious to see if he also treats this topic in that book as well; it'd be even MORE interesting to see this concept evolve over four books in four different genres.
UPDATE: I just checked the books and saw that Interface was actually published two years AFTER Snow Crash. Which is interesting; when I was reading it I kept on thinking, "Oh, this is a less mature version of Stephenson." Shows how wrong I was. Maybe this shows that "J. Frederick George," whoever that is, was just bringing Neal down? Who knows. It's also a new genre for Neal, although that hasn't stopped him from being brilliant before.