There are many references on delegation in the Getting Things Done book and in the Forums if you search on that keyword.  We have not done any Webinars just on delegation, but it's frequently mentioned in any recording that talks about processing and organizing.

In our coaching and personal experience in delegating to others, we also encourage people to delegate with "enough information so it doesn't come back to you with questions."   The Waiting For and Agenda lists are fantastic lists for tracking what you have delegated.