There are no new features that I know of in RC0 compared to those in CTP3.
For details of what's new in CTP3 (compared to SQL 2008 R2), see:
http://sqlcat.com/sqlcat/b/whitepapers/archive/2011/08/08/new-spatial-features-in-sql-server-code-named-denali-community-technology-preview-3.aspx