I'm just reading it right now. Almost half way through and loving it. I found the first 50 or so pages to be quite slow since I had to constantly refer back to the glossary of terms at the back. By around page 80, I started feeling quite comfortable with many of the terms and the reading became much smoother.
Loving the conceptual expositions and I certainly got a kick when I realised that many of the historical personages of Abre are all analogues of Greek philosophers.
The last N. Stephenson novel I read was "Cryptonomicon" when it came out and "Anathem" might well replace "The Diamond Age" as my favourite novel by him (conditional on the ending, of course, which I have great expectations for at the moment).