It depends, really. According to Alton Brown, from Good Eats episode #EA0917 "Raising the Bar":
"Now I know that Mr. Bond asked for his drink to be shaken. But you know, when it comes to clear ingredients that are going to be served straight up and that mix easily, I'd rather stir. If there was foggy or murky ingredients, I'd probably give them a shake. Or if there were ingredients that were hard to mix together, I would definitely shake them. But there's another reason I want to stir instead of shaking here. Shaking chills a drink far, far colder than stirring, and gin is an aromatic and it really starts to lose some of its aromatic qualities once it drops below 30. So I think that this is definitely the way to go."
Therefore: Gin martini--stirred, not shaken.
