Share 'Aluminum frames - failure modes? Life expectancy?'

Recently I found I had cracked my 3-year old Aluminum frame CX bike. Pretty bad. Both the down tube and seat tube, just above the bottom bracket. Shit happens, I know. Damn glad it wasn't carbon, but if it was carbon maybe it would not have failed, I know. But it got me to thinking  - With an aluminum frame, are there certain failure modes to be looking for? Should I be looking for cracks in area…