As managers, our manager training has taught us a thing or two about how to run successful meetings.  

We know that we need to keep them short, tightly focused, and limit the  number of people that we permit to attend. Our goal is to avoid having  to attend those time wasting events that seem to go on and on forever.  We know the drill: meetings should not last more than 30 minutes, we  should not invite too many people, and we should always show up with an  agenda for the meeting. However, not all meetings are created equal.  There are some meetings that by their very nature are going to be long  and complicated. 

How should managers go about handling these?