Depending on your unique business requirements, making a decision of whether you should host SharePoint on-premise or in the Clouds can be tough. We found the Microsoft SharePoint® Online Standard Service Description document, detailed and helpful.  Jump to Page 23 Appendix B for a feature comparison between Office SharePoint Server and SharePoint Online Standard and SharePoint Online Dedicated. Below is summary of Appendix B from the August 19, 2009 version of the document.
This helps break out of features by:
- Collaboration Feature Comparison
- Portal Feature Comparison
- Content Management Feature Comparison
- Search Feature Comparison
- BI Feature Comparison
- Business Process and Forms Feature Comparison
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