I never really used the selectors API's untill my customer wanted to add some special behaviour on the first tree cells of all rows of a particular table body.
In combination with YUI this proves to be a really cool feature.
Some new specs for my TO-READ list:
The snippet below selects the first 3 cells from all rows inside tbody[id='fileresults']
Below the macro which generates my table using jx-template (Apache Cocoon)