I previously suggested the warning for users submitting a question with only one tag on it.
Following up on that, I'd like to suggest another (relatively unobtrusive) warning to new users that suggests that if they are asking a question about their code, that they provide a dang code sample. How many wasted man-months happen every day due to people asking for help with their code and not showing it?
Maybe if it's the very first question they've ever asked, they could get a polite one-time Clippy™-style notice like "I see you're about to ask your first question. Did you: 1) Check your spelling and grammar? 2) Provide a sample of your code if you're asking a coding related question? First impressions are important!"
I know it's sort-of posted in the sidebar, but I think new users, no matter what the interface, always need some hand-holding.