A short while ago there was a short thread about parallel processing of XML. The well behaved processing of full hierarchical structures offers two unique characteristics and a unique opportunity; one for their automatic parallel processing and another for being processed in an almost total parallel processing fashion. This is particularly useful for processing XML queries that are accessing many different pathways in each query. These multipath queries are extremely powerful because they increase the value of the data by utilizing the goldmine of hierarchical semantics they naturally contain between pathways. They also require more complex processing logic that can keep multicore chips fully utilized with their parallel processing. 

Hierarchical structures and their basic principles of multipath query processing naturally map out the parallel processing pathways and their synch points allowing for complete automatic parallel processing. For full details, see the article below. It was one of a special report on parallel processing and multicore use just published from DevX.com. 

Automatic Full Parallel Processing of Hierarchical SQL Queries:
http://www.devx.com/SpecialReports/Article/40939/1954?pf=true