Now that Amazon SimpleDB is out, the open source competition has started and we can expect some pretty good stuff to come out soon and allow us to leverage this new cool tool from the AWS family.
I would personally be interested in a JCR adapter for SimpleDB: this would enable a semantically meaningful data storage layer to be plugged on top of the Amazon service. Think about massively distributed content management system...
Another cool idea, one that would really be dear to me, would be a RuleML fact base adapter for NxBRE. Since SimpleDB is built on Erlang, it naturally manipulates tuples, which are the essence of RuleML's atoms and facts. A fact base adapter would allow the rule engine to tap into a centralized knowledge base and make deductions out of it. Think about massively distributed expert system...
