I see "@Waiting For" as a temporary holding bin, for convenience only. Nothing sits in there for long. One thing I do during my weekly review is to convert almost all of my @Waiting For items into untimed reminders in my calendar.
For example, "3/16, Called Joanne re new licenses for the foo server" is a typical item in my @Waiting For list. It's there because I left Joanne a voicemail on 3/16, but I haven't heard back from her yet.
At my weekly review, something like the following goes on in my head: "Hmm... I haven't heard from Joanne yet. I need to follow up with her. Let's see, if I haven't heard from her by the... 21st, I'll give her another call." Then I put a reminder on the 21st like this: "Call Joanne again re new licenses for the foo server (last called 3/16)". I'll also append "(3/21)" to the project in the project list so that I know where the next action is in my calendar.