Enjoyed the book. The killer vines conceit was definitely jokey, and I'm sure Scott Smith knew this. For me, the vines were more of an estranging metaphor for being forcibly "returned to the soil-" the book's real terror came from the slowly dawning realization that the victims were in an [spoilish]unsurvivable situation[/]. The same story could have been told using other narrative devices (terrorist/hostage, desolate mountain plane crash, marooned on a raft with sharks circling, etc), but most of them come with pre-existing baggage that the vines don't.
I still can't see this working really well on film, though. One of the novel's biggest strengths was its depiction of the slow deterioration of the group, and I can't see that working in 90 minutes.