The wire itself is not bad – what is bad is where the wire meets up with the receptacle. Aluminum expands when it gets hot and contracts when it cools down. Over the years this expansion and contraction makes the connection to the receptacle loose. What then happens is that the wire starts to arc because the connection is not tight. Think of your spark plug in you cars engine. Also the wire itself starts to vibrate every so slightly but under heavy load it can get hot – really hot! It is not uncommon to open up the face plate and see a black electrical box and that the wire shielding/insulation burnt right off. The issue of aluminum wiring is not a myth or just a money grab on the part of your local electrician – it is real!
When we had our home converted there were many outlets that were black and burnt and giving off a tremendous amount of heat. It was only a matter of time before the load was too high and the heat to hot that we would have had a fire.