Currently, jQuery.fn.data() fires events (getData, setData, changeData) each time a data item is modified. This causes significant performance degradation (.data() is about 10x slower than jQuery.data()) but is rarely--if ever--used.
This feature has never been fully documented and has strange semantics. Let's deprecate it for 1.8 and remove it in 1.9. It can be implemented with a duck punch. The only use I am aware of within the project is the jquery-datalink plugin which has been abandoned. I don't see it being used in Boris Moore's jsrender code.