Let's think about the next scenario: I found a good domain name, i bought all the extensions (.com, .net, .org, .info). What's best for me from the SEO's point of view: 1. redirect the .net, .org, .info to the main one (.com) ? Or... maybe other suggestions?
From SEO point of view, there will be ZERO benefit if you forward the other extensions to the main domain. Especially since these other extensions will not be indexed (simple example: my xhtmlcoding.com domain is the main website, while the .net version redirects to .com, even tho the .net once was indexed before I purchased it now it no longer is). What you can do, is host the other extensions on different c-class IP's, build them as site of same niche as your main domain and possibly link them to the main site.
depends...if other extensions are same domain name and you are using 301 redirect, it wont hurt your .com, else it might. if there is any link juice for the extensions, it will now be forwarded to the .com