Tom Easton of Analog's Reference Library column is frustrated that Alan Dean Foster doesn't reveal the maguffin of Sagramanda until the very end, but concludes that, "No, I won’t tell you what the macguffin is. But I will say it is indeed one that would be valuable to society and to certain businesses, while other businesses might want to suppress it. And despite Foster’s coyness, he is such a deft and evocative writer that Sagramanda is a good read anyway. Enjoy it."
Easton's solution - to skip ahead to the end of the book. My mother does this - and sometimes my wife - but it drives me nuts. My own advice: read faster! The end will come sooner that way.
Meanwhile, for those not-in-the-know, a macguffin is a plot device that is used in film and other narrative (particularly mysteries and thrillers) to advance a story but whose nature doesn't really matter. The term is usually credited to director Alfred Hitchcock, though it may have been coinced by his friend, screenwriter Angus MacPhail.
In a 1966 interview, Hitchcock described the macguffin's purpose thusly (via Wikipedia):
"It might be a Scottish name, taken from a story about two men in a train. One man says, 'What's that package up there in the baggage rack?' And the other answers, 'Oh that's a McGuffin.' The first one asks 'What's a McGuffin?' 'Well' the other man says, 'It's an apparatus for trapping lions in the Scottish Highlands.' The first man says, 'But there are no lions in the Scottish Highlands,' and the other one answers 'Well, then that's no McGuffin!' So you see, a McGuffin is nothing at all."
Update: Neth Space also weighs in with a review of Sagramanda: "Sagramanda becomes a character all its own as we see a microcosm of India – the poor, desperately poor, the rich, the tourist, the huge population, the filth, the decadence, and the contrast of old and new – through the eyes the hunters and hunted. The portrayal of India is fascinating – especially for someone like me who has never been there. As I said about John Burdett in relation to Bangkok 8, I don’t know if Foster gets it right, but it feels like he does.... It’s a fascinating portrayal of near-future India with an average techno-thriller plot holding it together."