Productivity, enthusiasm, willingness to learn new tricks (get 'em in knowing PHP, watch 'em learn C, Java, and ASM as they go deeper into our stack), and willing to take the risk of sticking their neck out with outlandish but brilliant ideas.
This has typically arisen from working with existing OSS projects which incorporate vector transforms and the ilk in ASM, often badly or subtly brokenly, and from building optimised functions for doing fun things like creating n-dimensional maps of customer/product relationships in order to determine purchase propensity based on cluster profiles.
So yeah, ASM in a web shop. Except we're only kinda a web shop these days - client sites are our marketing platform, but our business is business systems.