Simon Fell > Its just code > API Cursor Storage Optimization
From the Sforce forums : To enhance the performance and availability of the service, Salesforce.com has changed the way that large queries are handled. Queries returning more than 5,000 rows will now be processed with a new architecture. Note that only a small subset of queries are large enough to be affected by this change. Existing customer integrations should not be affected in any way. If you notice any issues, please contact our support team.