Like you, I am responsible for delegating work.
I agree that using Outlook to delegate tasks is presumptious. It presumes that whomever you are delegating to uses Outlook to manage their own tasks. In my work environment, we use Lotus Notes, but I manage my tasks using a Pocket PC that is not sync'd with Notes. When someone delegates a task to me in Lotus Notes, it forces me to manage my tasks in two places. And since not everyone that I work with uses the "delegated" tasks feature, the use of Notes for task management is inconsistent. Whatever you do, do not force your way of managing action items on other people unless they ask you to do it that way -- it will only foster resentment.
I am responsible for delegating work to 10-20 people at any given time. Also, at any given time, each of them can be delegated 10-20 action items. That's 100-400 waiting for's! The way I stay sane is to use a real project management tool -- in my case Microsoft Project, but there are a couple of good open source/free alternatives that can help you to keep track of who is doing what and when is it due.
I limit my formal @Waiting For list to items that are not part of a formal project plan.
For example, a delegated action of "add a new user account to our revision control system" would go on my @Waiting For list because it is an ad-hoc request; not part of a formal project plan. Whereas, a delegated action of "write security framework for the Foo application" would probably be part of a project plan, so it would live in Microsoft Project.
Having these items separated can create some small amount of confusion -- which list did I have that item on? But a consistent weekly review (including a review of my MS Project files) along with a solid "capture habit" helps with that.