Release candidate 0 is now available for download (HT: Mark Riffey).

Also via Mark, here's the whitepaper on the changes in 2012. Features discussed include:

Availability Groups provides an integrated set of options including automatic and manual failover of a group of databases, support for up to four secondaries, fast application failover and automatic page repair
Failover cluster instances
Active secondary instances
Multi-subnet failover
Reduced patching downtime when run on Windows Server Core which is a low-maintenance bare-bones server install.
High availability for StreamInsight.
Performance improvements, including an in-memory column store, better full text search, up to 15000 partitions.
Auditing is improved, authentication has been enhanced with user databases.
Project Crescent "makes self-service reporting a reality by providing a highly interactive, web-based data exploration, visualization, and presentation experience to users of all levels—from business executives to information workers."
PowerPivot enhancements
Semantic search
Managed self-service business intelligence
Better SharePoint integration
Improved data quality management tools
Better integration across on-premise and cloud environments (Azure)
SQL Server Express Local Database Runtime (LocalDB) - this appears to be an embeddable SQL server.

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