Mac OSX, 10.7.4. Running Chrome.
As you can see, my bold text is... not very bold. There is a little difference though.
Happens to me in SciFi.SE only. SO is fine.
I tested with Safari, and it actually works, so perhaps it is a Chrome problem.
Why is this?
User phantom42 provided a good comparison of Chrome (top) and Firefox (bottom) on OSX: