Rob Farley in SQL Server Developer Edition versus SQL Server Standard/Enterprise excellently summarizes:
Developer Edition is just Enterprise Edition without the license to be used in a Production environment. Also, it doesn't need to be installed on a Server OS (ie, you can put it on Win7, Vista, XP).
Also, my experience shows that Developer Edition outperforms Enterprise Ed in the same equal conditions (on the same machine, etc.)
Why cannot MS SQL Server be used (or, even, installed) on workstation Windows (XP/7) in production?
I am interested in technical aspect of the issue.
Plz put licensing and ethical aspects outside of this thread (open your own if you feel up to