Great question. Unfortunately, I think the answer is "it depends." It will probably depend on your particular audience and the way they interact with your site.

Great question. Unfortunately, I think the answer is "it depends." It will probably depend on your particular audience and the way they interact with your site. What I'd suggest is an A/B test with a few different header link layouts. My guess is having the "Sign in" link at the far right is a good idea, since it's easy to find. But what do I know? The data you get from an A/B test will probably be more relevant than any guesses I come up with.