Holy crap! I just found out that Neal Stephenson's new novel is to be titled Anathem, and according to Amazon, it's set to be released on September 9, 2008. Also, it's 928 pages. I don't know how I missed this, but apparently, some details about the novel leaked last September, in this LJ entry:
He's writing a science fiction novel unrelated to Cryptonomicon and the Baroque Cycle. It's set on another planet and has aliens and so on. It's really about Platonic mathematics, but he needed the aliens and space opera-ish elements to spice it up a little bit, just like the pirates kept people engaged in the Baroque books. He's nearly finished writing it, and if he doesn't finish by the end of the calendar year he'll have to give some money back. If everything proceeds according to schedule, it should be available in stores in about a year.
Damn! Looks like my US Civil War era prediction was a bit off, though I do think my prediction is still in place for the next Cryptonomicon/Baroque Cycle style novel will feature at least one portion set in the US Civil War Era. Or something. In any case, I'm psyched. (via this wikio page I found in my referrers)

Update 3.31.08: Lev Grossman, geek blogger for Time magazine, reports on the plot:
Since childhood, Raz has lived behind the walls of a 3,400-year-old monastery, a sanctuary for scientists, philosophers, and mathematicians—sealed off from the illiterate, irrational, unpredictable "saecular" world that is plagued by recurring cycles of booms and busts, world wars and climate change. Until the day that a higher power, driven by fear, decides that only these cloistered scholars have the abilities to avert an impending catastrophe. And, one by one, Raz and his cohorts are summoned forth without warning into the Unknown.
Interesting. No mention of other planets or aliens, but a promising plot, I guess.