"It's also worth pointing out that writers don't have any say in casting. Occasionally we get a vote but it's only a vote."
Neil Gaiman, "Why I won't do homework".
Sometimes we get asked our opinions, and sometimes we can even think of people. Clive Mantle, for example, sprung to mind 'cos I knew it'd please my mum.
ETA: You might like to read my comment on Neil's talk in London last year, or on his Anansi Boys.