I found competing views on the internet. At first it seems that everyone says you shouldn't eat chicken if it has any pink at all, and then I found someone who looked at the evidence and talked to scientists:
I spoke with a number of poultry scientists and discovered that while it's plausible that salmonella (a bacterium that, by the way, is hardly unique to chickens) could show up on a chicken's skin and contaminate cutting boards, the chances that it works its way inside a muscle, like the breast, all by itself? Very, very slim, and really no different from the odds of E. coli camping out in a medium-rare steak. The Centers for Disease Control has documented five salmonella outbreaks this year, none of which involved eating chicken.
Read more at Esquire.com
So, from now on I'll cook my chicken medium to medium-well, when I cook for myself. If I cook for you, I'll ask how you like it.