The light blue color (less so for visited links) and the very slender font face hurt readability, especially on laptop screens which are sensitive to viewing angle. It is merged into the white background very easily.
The font, color scheme etc used on Bitcoin.SE is a standard theme for all SE Beta sites and is not under the direct control of the moderators here. That said, I can bring this up to an SE employee if enough people feel it's a real problem. I'll let the upvotes do the talking.