So now that the next James Bond movie has been officially announced as Casino Royale, what are the odds of them actually using the plot of the novel? (One way or another they'll probably use more of it than the 1967 movie of the same name.) Obviously, unless they plan to set it in the '50s or '60s, they can't use the Cold War elements of the story, and they'll have to pump it up with more action sequences. But the basic story, villain (Le Chiffre) and Bond girl (Vesper) are pretty solid foundations for a movie. And given the current popularity of film noir and offshoots thereof, it wouldn't hurt to keep at least some of the book's nods to hard-boiled detective fiction.
It'll help if the filmmakers could have the patience, or faith in the audience's patience, to make the baccarat game an important part of the movie and rely on the game to create suspense and tension. The makers of Goldfinger kept the golf game, which does much the same thing, but I've noticed that people of my generation (including me, the first time I saw it) get a little restless during the golf game; we're waiting for something to happen, and the sustained tension between Bond and the bad guy doesn't always strike us as meeting that standard.
The movie would do best to follow the plot of the novel for one basic reason, which is that that's what produces the best Bond movies. The Bond movies that actually use the stories of the books they're based on are Dr. No, From Russia With Love, Goldfinger, Thunderball and On Her Majesty's Secret Service. (You Only Live Twice would probably have used the story of the book if it had been made after OHMSS, as originally intended; since it wound up being made before, the book's plot had to be dropped because it's a direct sequel to Secret Service.) Some of these are more faithful adaptations than others, but they're all recognizable if you've read the book, whereas most of the others just use the title and a couple of character names. A movie adaptation has to add something to the Fleming books, of course -- humor, most obviously; more action scenes; maybe even some changes to smooth over Fleming's logic gaps (eg changing Goldfinger's big plan from something that's literally impossible to something that's vaguely plausible). But based on the track record, there's not much doubt that the Fleming plots are the best starting point for a strong Bond script.