They've been making the CMoy headamps in Altoids tins for a long time. They didn't start in the tins, but kind of went there for the novelty factor. The CMoy (named after the designer Chu Moy) sound surprisingly good for what they are. There are quite a few variations on the theme from different opamps for different sounds and even mini vacuum tube versions that will fit in a tin.
I've built several and I've never had anyone that's listened through them not like it more than just coming direct from the source. I think they are an excellent way to get your feet wet in the DIY headamp scene. It's almost a rite of passage.