Waiting for -- what level list?

Dear All,

I was thinking about "waiting for" items. Is that a "project level" or a "NA level" list? The problem occurred to me when processing emails I send -- I am waiting for an answer, which could come in 30 seconds, if the partner is on-line, and could come in two days or a week, if they are on holiday. Now, in the first case, it is enough to jot an item to the waiting for section of my NA lists, while in the latter, it is rather well placed among a list in projects. Or, for that matter, it could go to my diary. What do you think? (And, of course, I mean that I don't know when the answer would come.