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#21
MSDN is for developers, TechNet is for IT. MSDN is a "higher" level than TechNet: depending on the MSDN level, you could get a lot more software with MSDN (including stuff like MapPoint, Streets and Trips, Visual Studio, Expression Studio, etc), and the MSDN licenses are less restrictive, too: TechNet is limited solely to evaluation, whereas MSDN allows for testing, development, and demonstration. So if you have a computer whose sole "production" purpose is to be used for software development, then you can use a MSDN license on it for "production".
(Also, of the Office licenses you get from MSDN, one of them can be used for "any purpose" without restriction; TechNet does not get this perk.)
But for all of MSDN's awesomeness over TechNet, it's also much more expensive, and the people who have them are usually developers who get it through their work.