I don't think any one thing defines it - it is ever evolving. For the long timers who have been here for ~4-5 years have seen this evolution. In the beginning it was about eeking every last bit at any cost (was always my goal), everything else be damned. As time has progressed, new products arrive and old stereotypes get disproven. For me personally I am more about the notion of great performance with little noise. The latest trend here at XS seems to be a contest as to who can be the most outrageous with the silliest gear and spend the most money. Some folks go against logic and all that was learned over the last 5 years just to try to be extreme. Anyway, that's my .02