Hi,
The main difference between SQL standard and enterprise is still on scalability and BI parts. For example, the 2 nodes limitation on clustering.
As I known, there is no special ESB feature depends on features that SQL enterprise has but standard not.
For your reference:
2008:
http://msdn.microsoft.com/en-us/library/cc645993.aspx
2005:
http://www.microsoft.com/sql/prodinfo/features/compare-features.mspx?PHPSESSID=0324345d45ef1bf1f764044e03584cd0
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