The word eucalyptus comes from the Greek eu "well", kalyptos "covered" and refers to the buds of the flowers of this tree.

The story of the eucalyptus is similar to that of many immigrants. Originally from Australia, it "migrated" to other regions growing even where natives trees didn’t. In this way, it also covered Ethiopia with its characteristic scent.

It’s another one of those polemic trees just as the jacaranda, because it adapts very well to almost any region dominating over the natives species; conquering deserts as wells as swamps. Depending on who you ask, some people consider it a curse, and others a blessing and as it usually happens the truth is in the middle point.

Everything started in Australia where the eucalyptus is original. According to the local legend, in the beginning of times there were a group of natives Australians that were gathering wood to make a fire. They picked up different kinds of branches and they were getting everything ready when they heard a particular sound that scared them. They stopped what they were doing because first they thought it was the sound of an evil spirit; but since the sound was pleasant they realized it was the the spirit of the wind blowing through a branch of eucalyptus hollowed by termites.This was the origin of the didgeridoo, an instrument that is used in rituals to connect with the spirit of the ancestors.

The eucalyptus wood is still being used to build these instruments but besides that this tree has many uses, especially in the medicinal field.
The oil is used as a stimulant, antiseptic and aromatizing.
This tree has more uses than any other tree; for example covers empty land from marshes to mountains, it provides shade and acts as a windbreaker. It provides resin, nectar and gum. When cut is used as fuel, in construction, poles and furniture.
In Argentina there are also many of these trees, and I remember that when I was a little girl we used to go with my family to the country in the outskirts of Buenos Aires and gathered leaves that then my mother boiled in water to scent the house and disinfect the air and also as a decongestant when any of us had a cold.

In Ethiopia it was introduced around 1895 because of the deforestation around the new capital Addis Ababa caused by the use of wood as fuel. The Emperor Menelik II approved its plantation in the city.
The great advantage of this tree is that it’s a fast grower, requires no attention and when cut grows back from its roots and can be harvested every 10 years.  The eucalyptus is a definite element of Addis Ababa, a city scented by the perfume of this tree.

The arguments against the eucalyptus, is that destroys the native vegetation, consumes too much water and ruins the soil, among other things. But it seems that these arguments are only partially true.
My personal opinion is that first we should try not to destroy the native plants of each region, something that rarely occurs and in general we realized what we have done when it’s already late. When you can reforest with native trees, one should try it, but sometimes this is not possible or a faster solution is needed. In this case I consider that the eucalyptus is welcomed mainly because the lives of many people that otherwise would probably be starving or dead depend on it.
Nobody questions when we plant corn or wheat and we use precious resources to grow these crops; sometimes a forest is as valuable as a field of any edible grain.
In Ethiopia eucalyptuses are an important source of fuel and prevent the erosion of the soil and I really prefer land planted with eucalyptuses to sterile deserts.

Here there are three articles about this subject:

Las bendiciones de un árbol maldito (in Spanish)
Is Eucalyptus ecologically hazardous tree species? (in English)
The Eucalyptus - How Useful Is It? (In English)

There is a book by a Canadian writer that tells his memoirs when he was living in Ethiopia with his missionary parents, and it’s called The Scent of Eucalyptus: A Missionary Childhood in Ethiopia and was written by Daniel Coleman. There is another book from a Irish writer that also narrates his adventures in Ethiopia in the 60s titled The Scent of Eucalyptus. An Ethiopian Tale by John Dillon.

Since I always like to leave a "gift" here goes a poem by Evaristo Ribera Chevremont, a Puerto Rican poet (translated from Spanish):

The Eucaliptuses

I see the eucalyptuses taking the hill,
where the Tropic reduces its wild violence.
More than light, beneficial vapor lightens them.
They are the pleasant form of benevolence.
Their branches shake, nurtured by the essence
that the air in the deep space spreads.
The generous earth, the earth of excellence,
its perennial bounty creates.
And what a splendor! Heavenly good,
the trees are full of juices and scents.
Prodigal eucalyptuses in the diurnal flame.
I receive their abundance of juices and scents,
and I feel full with all their favors.
Under the eucalyptuses goodness claims me. 

AliciA