I just re-read Neuromancer for the third time (and Count Zero and am working on Mona Lisa Overdrive) and was thinking about the potential film in context.
Hayden Christensen is not a bad choice for Case, really. His acting is a little wooden but a good director can get more out of him. remember, when we meet Case he is a burned-out junkie hustler with little more than his instincts going for him, a stray dog looking for his next meal and who he has to bite to survive. As he cleans up, he is still a little flat, almost pathetic, so much so that he has no sense of what is going on around him. This is all within Christensen's range. His role in Broken Glass shows a bit more depth than that he displayed as either Anakin or the character in Jumper.
However, we have to really look at Molly as the "star of the show". she is the one who has as much control as anyone over her own destiny.
Also, the Finn is huge, not only because of his own self, but the various "Finns" we meet along the way.
As far as any possible failure of film to reflect Bill's work based on previous efforts (I take the familiar designation by way of following convention, not that I know the man personally), we must recall that he himself had a great deal of input into Johnny Mnemonic, which I did enjoy, regardless of Keanu Reeves' wooden interpretation or the growth of Johnny proportional to the diminiation of Jane/Sally/Molly.
All that said, I saw a perfect Molly in a film last week - Emily Blunt - in a film called Wind Chill . She did a nice "Sprawl" accent (she's Canadian, I think, but still managed to sound like she was from Delaware) and has a face that would still be striking even if her eyes were completely covered by mirrored lenses. It is essential that she not have some bogus contacts - it must look like mirrorshades. Ms. Blunt has enough facial characteristics to stand up to having her eyes concealed. Many people are dependent upon their eyes for their beauty and with them it just would not work. In this respect, she is much like a younger version (but in her own right) of Angelina Jolie.
The Finn - once upon a time I saw Harry Dean Stanton as the Finn, but Harry's getting a bit feeble and in my re-reading I saw someone new - Steve Buscemi. He's really perfect for the part. I can just hear him saying, "I gotta pair of shoes older than you are."
Riviera - I see Jude Law.
For the Flatline - once I thought Kristofferson, but now I think Billy Bob Thornton.
Armitage/Corto - once I would have liked that part to be Ah-nold (before Total Recall happened) but now I see Christian Bale. I think he could do an excellent job of unraveling over time in a believable manner.
For music, I would use Robert Rich. His ability to create surreal electro-acoustic landscapes would fit the crumbling urban landscape as well as the equally seedy orbital environment.
One more thing - in the forward to the 25th anniversary edition, Bill mentioned hardwired payphones no longer existing. However, there was a war at some point. What if cellphones are made illegal, and the bandwidth they once used seized by governments, or even Turing, for that matter. Then, when Molly and case go into the Finn's junkshop, case and accidentally knock over a box of scrapped cell phones and someone can say, "they used to use these, didn't they?" and the other can say, "Not as stable as a land line."