It depends on what the @WaitingFor item is. If it's a task I've delegated to someone or I'm relying on someone to get me information for a next action, then I put that on my calendar as an all day event to trigger me to go back to that person sometime that day as a follow-up. If it's a broader, or less time sensitive item, then it's on my tasks lists with an @WaitingFor context. I'll typically check my contexts list 2-3 times a week.