A good friend of mine who has been in big corporate IT for a long time once told me that if his staff didn't know a lot more than he did, he was hiring the wrong people.

This is a hard lesson for managers-in-training, basically that the best people to hire are the ones that you think are smart enough to challenge you. Would you want your staff dumb enough to do your bidding without question? That only works for manual labour, where staff are extensions of the manager's body, but in technical work the staff are extensions of the manager's brain. The staff must know more than the manager for the manager to be effective in carrying out his group's tasks (and make him look good).

Unfortunately this is not how it works in real life, as managers do tend to feel threatened by smart people. You will find plenty of stories in which the manager did things that clearly demonstrated a lack of knowledge, and impeded the work as a consequence. A good manager need not have all the knowledge, but he needs to trust the knowledge of the staff and use that to make decisions.

In summary, the best managers are the ones that listen, think, and act. The annoying ones do only the latter two, and the worst just act.

As an aside, a big hear hear for The Mythical Man-Month as a great book to recommend to any manager.

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I'd like to be able to assign to an luser