I’ve been approach by clients several times about what they should do with their old domain, now that they finally acquired the domain of their dreams. For example, I own “company-1.net” and after 5 years of branding and Google indexing, I finally got “company1.com”. Now what do I do with my old domain?
301 REDIRECT! 
Tamar Weinberg wrote a quick blog on this approach today, “Don’t Let Your New Domain Hurt Your SEO” that I couldn’t agree more on.
The issue is that you should implement a 301 redirect. Otherwise, if both sites rank (as in this case), your redirected site might outrank the site with all the content. In this particular user’s case, an .edu site is outranking a .com. Chances are, the .com was also below the fold and the .edu wasn’t. You certainly don’t want to do it that way.
If you want to minimize your hit with the Engines this is the best route to take. Otherwise plan on it the road ahead being long and bumpy .

You mean some people DON’T use 301s?