There's a.. 3.9% colour difference between the background of code and the default answer background (245 vs 255) - could this be made a little easier to see?
For code it's not too big a problem, it stands out due to the syntax highlighting.. but block-quotes (someone elses words most likely) look very similar to the rest of the question, aside from a slight indentation..
Perhaps a subtle border would help?:
Edit: The way SuperUser does this is great, could it be extended to the other sites?