How about a difficulty rating for questions?
When browsing the questions I feel I can answer, I am often frustrated by the fact that there are questions above and below the level I would like to address. I wonder whether people feel we should have a "toddlers pool" for beginners to ask questions, and more "pools" for intermediate and advanced? I see a problem with the definition of the limits of each pool, but I imagine that posting a beginner question in the advanced pool is going to see it thrown out or drowned by the professionals trying to discuss more advanced topics.
This is a dimension I have not seen in the website and although it could be solved with tags, it's be better done separately.