Generally aluminum wire is not a problem as long as it is terminated properly, that where the problem is, we have a subdivision that all the houses are done in aluminum NM, and while it was a great service call area, I have done a few retro fits to some to re-do all connections, basically leaving the cable in place but making sure all connections are done to spec.
Here are some pointers when dealing with aluminum:
As said older aluminum will corrode, so using wire nuts with the dielectric grease in them will prevent this as well as allow you to change from aluminum to copper, Ideal DB twisters are such listed.
Aluminum expands much more then copper, and if put under just a set screw brass or copper terminal it will cold flow as it expands and will loosen when it cools off,
where terminated in a pressure type connector, make sure the connector is a pressure plate or has the spring type washer or plate under the set screw, it is important to only tighten the connection to the listed pressure, or you will cause the aluminum to cold flow out, breakers with aluminum terminals with set screws should be ok, but make sure it's not just plated copper as some are, anywhere else change over to copper wire before termination.
When hitting receptacles/switches with brass screws, use the twister aluminum to copper pigtails, or replace the receptacles with clamp type plate terminals, use plenty of anti-oxidant, at all connection, or a good dielectric grease, the latter doesn't dry out like anti-oxidant can.
Almost all failures of aluminum wiring can be explained in improper terminations and connections, some failures are because of the conductor being nicked when stripping, it is imperative to make sure to not nick the aluminum conductor when stripping, I will use one wire size larger then the conductor and pull off the insulation with my linesman,, I have yet to have a call back on any of these houses that I done, and the home owners are amazed at the money I saved them from doing a complete rewire, for the most part as with copper I have only seen a very few times where the wire failed in mid run, and even then it was attributed to rodents such as squirrels or mice.
