Hi Leon
there have been some significant enhancements to MySQL Cluster over the past 2 years, best demonstrated by the latest Development Release of MySQL Cluster 7.2 which includes Adaptive Query Localization - a technique which pushes JOIN operations down to the data nodes to dramatically improve the performance on complex queries
There have also been a number of enhancements in disk handling and heartbeating which enables MySQL Cluster to perform more predictably and resiliently if the underlying hardware starts to misbehave!
Would recommend reviewing the DevZone article on MySQL Cluster 7.2 to see whats new:
http://dev.mysql.com/tech-resources/articles/mysql-cluster-7.2.html
And also take a look at the Evaluation Guide which provides guidance on determining if Cluster is the right choice, and best practices in building a PoC:
http://dev.mysql.com/downloads/MySQL_Cluster_72_DMR_EvaluationGuide.pdf (note, opens a pdf)
In terms of sharding, MySQL Cluster does this for you automatically at the database layer, eliminating the overhead of implementing sharding directly within your application
Hope this helps - and don't hesitate to contact the forum for any further questions