We occasionally need to notify users about warnings or problems. But often times, especially if it's a common problem, users will just dismiss the warning and continue. Often times users won't even remember seeing the warning, but we check their logs and see that several were displayed. So, how do you get users to pay attention when you're trying to tell them something important?
This isn't as simple as forcing users to resolve all problems before allowing them to save. They often need to save data that isn't strictly okay by our business rules for various reasons (usually for problems that can't be solved right away, or at all).
We've got a better warning/error handling system in mind that I think will help a lot, but I want to see what others have done.