What's with “He-Who-Must-Not-Be-Named”?

Question

Right from The Philosopher's Stone to The Goblet of Fire, as far as the Magical Community was concerned, "The Boy who Lived" had lived while Voldemort had been defeated.
It's understandable that Voldemort had created for himself quite a reputation as a evil wizard whose very name made people shudder.
but once he was "dead and gone" , why worry? Surely, his name wasn't "taboo" at that time. The Death Eaters couldn't track the people who said his name openly.

Answer 1

A few things to consider:

1. Voldemort may have been defeated, but he still had a following of loyal Death Eaters, including a number of witches and wizards that were almost as evil and powerful as he was (that's paraphrased from one of the later books, though I can't recall exactly which, and don't have the books on hand to even begin searching for an exact quote).

2. Not everybody believed he was gone for good. Dumbledore, some of the Death Eaters, and likely other knowledgeable/powerful members of the Magical community, all suspected that he was still alive in some form, and would attempt to return.

3. Voldemort was the most powerful dark wizard of all time, and his memory alone was enough to terrify most witches and wizards. They felt safer not using his name when he was at the height of his power, and I imagine that same feeling of safety continued when he was gone as well.

4. In one of the earlier books, Dumbledore says that fear of a name merely increases fear of the thing itself (again, paraphrasing); they weren't scared only of Voldemort, the name was enough.

Answer 2

Aside from excellent reasons discussed by Anthony, a fairly Medieval-thinking Wizarding society was also quite likely follwing the old English proverb of "Speak of the devil and he doth appear".

Answer 3

Technically, Voldemort wasn't dead until Harry finally finished him off during the Battle of Hogwarts. Although he didn't have any physical form, he still was alive and in exile. Of course, few actually knew about this, but all things considered, people knew he was quite powerful and probably even knew that his obsession during his life was to become the master of death, and by his definition this meant to never die, to achieve immortality. People were (rightfully) paranoid that he would return, and they didn't want to risk becoming his victims.