I keep just one Waiting For list (actually, it's an @waiting context). The things I've found it important to track, however, are the name of the person for whom you're waiting as well as the date you requested action from them. That way, when I'm reviewing @waiting, I can easily figure out if a project has been dormant for too long, and who to contact in order to get it started again.

My @waiting list is very closely related to my @agendas, and if I know I will be meeting with someone soon I'll often move tasks from @waiting to @agendas so I can bring the pertinent project up when I next see them. Incidentally, my @wife list (actually labeled with her name, of course) is basically a concatenation of agenda and waiting-for items I'd like to discuss with my spouse at the next opportunity. You may want to set up your own individual agenda/waiting-for lists for people with whom you have constant contact.