Having just come from a meeting where, I'm afraid, I was guilty of rambling on in a sub-optimally productive manner (sorry, Allen and Alison), this post from 37signals hit home, especially this article about how Google runs meetings. They're as short and as focused as possible, use a big clock on the wall (I need to get a large-display portable timer!), use a projector for note-taking, schedule micro-meetings (5-10 minutes instead of 30, say) and carve out office hours that people can queue into on a FIFO basis.
That's one extreme end of the meeting spectrum. I believe it's called an action meeting. I wish we used it more at Olin; one of the things you hopefully pick up here is how to run an efficient, effective meeting, and the folks at Google sound like they've got that down cold.
Of course, we've got to acknowledge our need to be inefficient equally often. Paradoxically, often the most efficient way to do things is to schedule unscheduled inefficiency, since we need to be rambling humans once in a while. (It's the same principle behind letting yourself sleep nights; you get less work time, but you get more effective/alert work done.) Sometimes you need a raw data dump, not a productively focused discussion. Sometimes you need to pitch the agenda and dialogue with other humans on a personal level instead of whizzing through a list with everyone staring at the projector screen of notes. This is called a dialogue meeting.
It's important to know whether a meeting is dialogue or action at the very outset (or when it transitions from one to another). By giving ourselves permission to be inefficient, we allow ourselves to focus when we want to be efficient, and vice versa. The mark of a good mentor (at least among engineers) is that they're efficient and productively focused with their time - optimized, so to speak - but that they are willing to waste time for you. You both know what they're giving up, so the time and the teaching are precious, the same way lying down for a breather feels so much more delicious and satisfying after a 2-hour run. I believe the same holds true for meetings.
Use your time wisely. Use it optimally. And know that part of a wise spending of your time (or money, or energy, or anything -) is to allow yourself to "waste" it.