There are some great posts summarizing this wonderful development effort of updates, features, fixes and new!

Bullets of Interest

• Developers? There is a new SDK
• Visionaries? Dynamics CRM with MarketingPilot and NetBreeze
• Features : First there was Decembers R12 Polaris and then RU13

Links for More

• The CRM Team Blog summary
• Upgrade Instructions
• The Download Center
• Studying and Extending Dynamics CRM -> Dynamics xRM
• The Report Authoring Extension
• Connecting the Data is talking about it
• Amreek Signh is talking about it
• The xRM.com Writing Team is talking about RU13
• Donna Edwards talking about RU13 Including a Great little Video!