As a hard rule I'll never be impaired at work or anything like that, though on my personal projects I've found slowing drinking a glass of a good rum is a very useful aid to programming. As others have said there's a wonderful objectivity to programming, you can't really blag it when you're working with others as I am on the personal project. I think it's the lack of inhibition that helps, it's telling the voice in your head to shut up with over-engineering things and just get to the instant gratification of a panel of green tests and features that work.

Debugging while inebriated is another thing altogether, that's no fun at all.