On the projects I do it usually specs that aluminum wire shall not be used in sizes smaller than #8 awg. Even then they need to be in a compression adapter before inserting it into the termination. The NEC does allow both feeders and branch circuits to be in aluminum but I personally wouldn't do it.
Years ago, aluminum wire was used because of the cost benefit, but it was discovered that people were not stripping it properly nor were they putting it under cl/au terminals. This caused loose connections and then fires.
Although insurance can be problematic on houses wired in aluminum, you can get insurance on them. If cared for properly, as in retorquing connections and using noalox, you can have a safe installation on branch circuits.
Example of compression adapter: http://www.wescodirect.com/direct/Pr...oductId=141622