Merlin Mann, the self-described "head basket case in charge of productivity on the Internet," started his presentation at Macworld Expo this week by thanking his sound engineer. He finished up by offering to share his Altoid mints with everyone in the audience. In between, he gave a funny and insightful talk on how to take control of your own time and attention.

Mann is a blogger at 43 Folders, which provides tips and discussion for people looking to maximize their productivity. He's been a main driver in the popularity of a self-help personal-productivity book and philosophy called, Getting Things Done, by Dave Allen.

Unlike other self-help programs, which try to make you more spiritually evolved, or change your entire focus on life, GTD's goals are more modest: It's a system of small steps to get your life organized, reduce stress, and prioritize the tasks you have to do -- from small things like taking out the trash to big things like starting a successful business.

"A lot of these motivational speaker guys with big teeth like to talk about capital letters like Values and Excellence. I don't even know what Excellence is," Mann told an audience of Macworld attendees. "But you can take measures to achieve modest goals, like getting home at a reasonable hour and not spending all weekend catching up on e-mail."

The key is to take charge of your own time and attention, Mann said. Don't be too quick to give other people the authority to boss you around, and don't take on habits like reading RSS feeds, fiddling with Facebook, or watching TiVo, if those habits aren't providing you with any value.

Sounds simple -- but most people don't really have a handle on how valuable their time is, Mann said. If a co-worker approached you in the hall and demanded $100, you'd give him the brush-off, because you know how valuable $100 is and you know what it feels like to lose $100. But the same co-worker can drag you into a meeting that wastes your time -- a resource that, like money, is precious and finite.

"When the value of your times is set too low, or not at all, it leads to waste and abuse," Mann said.

This is a particular problem for knowledge workers. (How do you identify knowledge workers? "Look for someone with girlie smooth hands who can go to lunch whenever they want," Mann explained.) Knowledge workers have huge amounts of freedom in how they work, they aren't micromanaged, they just have goals to achieve. That freedom is dangerous. "You can find yourself at two in the morning staring at Wikipedia covered in pizza crusts," Mann said.

Knowledge work jobs are "black box jobs," he said. If you're a knowledge worker, inputs go into you -- people give you specs, you go to meetings, you take in e-mail -- and the product comes out. You're the black box in the equation -- your colleagues and managers don't know how you work, and they don't want to know.

Moreover, knowledge workers have complex reporting relationships. "How many of you are doing exactly one job for one person?" he asked the audience.

Knowledge workers have a lot of dotted-line reports and relationships at work, and managing all those relationships is part of keeping the black box running. "Boss #7 does not care that boss #3 really wants something done," Mann said.

Decisions on where you allocate time in that matrix have opportunity costs -- if you're doing one thing, you miss an opportunity to do something else. He showed a photo from the set of the old TV show, Let's Make A Deal, to illustrate the point. "If you choose Door #2 you don't get to see what's behind Door #3, which is really a shame, because that's where the donkey is," he said.