Sometimes browsing a tag or search term combination is a good way to get an overview of a subject. But going through the Q&A is a bit labor-intensive because you keep clicking back and forth between the list of hits and the individual questions.
So let's say you search on something...like
[c++] and [lock-free]. Then if you drill down into an item in that list, it opens the page, but remembers the position in the list you were in. (Using...cookies or crackers, or whatever web-magic.) Then offer navigation within the list to go to the next or previous. Stepping off the end of the list either way could take you back to the list itself.
This would be useful if you're just surveying Q&A to try and get an overview. Basically flipping pages on a sort of weird custom e-book on a topic. (Ctrl+?)Left and (Ctrl+?)Right seem like they would be great, but even if it were buttons it would help. The buttons could be on some navigation element showing you what the query in effect was on the page (so it isn't an "invisible" piece of state).
Previously there were suggestions for using the left/right cursor keys to seek to the next or previous answer on a single question. That doesn't seem too useful to me, personally, as you should have vertical scrolling sorted out some other way already (mouse wheel?).
There's also a request to use left and right to navigate between the numbered pages of results. That isn't contentious with this suggestion...though it doesn't seem as important to me.