Originally Posted by General Geoff

I've never had any issues with bottom bracket threading on my aluminum bike frames. and there are millions of aluminum engine blocks out there that make hundreds of horsepower dependent entirely upon the strength of the threading that holds the cylinder heads in place. While correct torque specifications are arguably more important in aluminum threading than steel, the resultant mechanical fastening can be just as robust as if you were threading into steel.

Oh and I also have two aluminum-framed motorcycles that endure far greater stresses than any bicycle which have gone over a hundred thousand miles without any stripped threads or stress failures. The material is about as sound as you can get from an engineering perspective.