Often, I want to highlight & copy the contents of a single posted code block so I can paste it into my IDE for a better look or into my answer for editing. This gets awkward especially if there's scrolling involved -- I usually overshoot the end and trying to shift-arrow back into the code block just overshoots in the other direction.
I agree, so I wrote a bookmarklet that puts a copy button on top of every code block.
It is going through Code Review now: Bookmarklet for selecting code snippets on Code Review
Some excellent suggestions were made and it got turned into a CR repo :