Now that Neal Stephenson's The Confusion is out I have to say I never managed to finish Quicksilver.
Part of the issue is length: 944 is a lot of pages. But a lot of it is editing. The book is just too much. Too bloated. There are some really cool ideas in there, and some fun research, but it's buried deep in the 944 pages. I finally checked out entirely after the second book about Half Cocked Jack. I kept waiting for something relevant or interesting to happen and it didn't.
I like Stephenson's writing. I thought The Diamond Age was brilliant and Snow Crash has a lot of interesting ideas in it. I even managed to get through Cryptonomicon, although it suffers from the same bloat as Quicksilver.
Maybe he needs fierce editing? Maybe I need patience.