"Since the Introdus in the twenty-first century, humanity has reconfigured itself drastically. Most chose immortality, joining the polises to become conscious software. Others opted for gleisners: disposable, renewable robotic bodies that remain in contact with the physical world of force and friction. Many of these have left the solar system forever in fusion-drive starships.
And there are the holdouts: the fleshers left behind in the muck and jungle of Earth—some devolved into dream apes, others cavorting in the seas or the air—while the statics and bridgers try to shape out a roughly human destiny."
Egan's books have been some of the most thought-provoking I've ever read as far as science fiction technology. A lot of the works were out of print until recently; I'm glad to see there's been a resurgence of interest in his writing, and the availability of his works.
http://www.amazon.com/Schilds-Ladder-Novel-Greg-Egan/dp/1597...
Although it's more like Schild's Ladder than Permutation City, I suppose. (Physics ideas rather than computation.)
I'd read Schild's Ladder prior to reading Permutation city, which is also a good read. It does seem to get bogged down in the technical and descriptive side of things at times, however, it's a fantastic idea for a story. The main premise of the film would make a great movie.
Whilst I'm on the subject of good "Hard sci-fi" novels, Tau Zero is also worth reading.
Edit - I'll also throw this in: http://www.amazon.co.uk/gp/product/0814703259
Magic :-)