I've been in Portugal a year ago and people told me to be aware of that rule while driving, otherwise I could be fined. But I drove from Lisbon to Leiria through Autoestrada A1 and I still saw some cars driving on the left and overtaking by the right, so I think that, even though the rule is really good, it's not being sufficiently enforced (or, maybe, the drivers on the left were all Brazilians!).
I don't understand what rule you were told to be aware.
The highway codeis pretty clear and says that you must allways drive on the right lane! The other ones are only used for overtaking. Sometimes different lanes take you to different places and of course that on that case you should use the one that suits. In traffic jams of course that every lane is used.
I leave near Lisbon. A1 is the highway that connects Lisbon and Porto, the two biggest citties in Portugal. From Lisbon until Torres Novas each direction of the highway has 3 lanes (more up north I don't know very well). It's very common to find idiots in the middle lane with the right one free of vehicles.
It is also stritcly forbidden to overtake vehicles on the right side. Overtakes should allways be made through the left. Some exceptions exist. For example, in traffic jams, if the right lane is faster than the left one, these vehicles are not overtaking the other ones on the right.
But (lawyers love these things) the highway code doesn't have an explicit definition of what an overtake is. Some argument that in order to overtake someone, one needs to be behind him, use indicators to show your intention, change to the left lane, overtake the vehicle and return to the right. If you are driving for miles and miles in the right lane and see an idiot alone in the middle lane, some argument that if you just stay where you are you are not overtaking the vehicle, your are passing him.
In Germany, from what I see on YouTube, drivers are much better behaved. You can see videos from someone driving fast on the Autobahn and others vehicles are on the right lane.
