- Algorithm and data structure concepts
- Design patterns
Algorithms, data structures, and design patterns, in my opinion, belong on Stack Overflow. This is especially true considering that "specific programming problems" (design patterns are potential solutions to these) and "software algorithms" are on-topic on SO. I would also suspect that "higher-level" (meaning above and beyond implementation specifics) would probably be more suitable to Theoretical Computer Science or Mathematics, depending on the specific question.
- Quality assurance
The SQA Stack Exchange is now in public beta. Feeding QA questions to them would probably be beneficial to their community. In fact, according to their Area 51 stats, they could use some more questions and visits per day. We should show them some love.
I think that the FAQ should also be more specific about tools (IDEs, editors, libraries) belong on StackOverflow.