This has been a big issue with so many webmasters; they always demand to get links from EDU or GOV websites. I have seen so many clients arguing over that try to build links from those websites which are from gov or edu.
I have lost one job for that reason as well, client was asking for links from gov and edu websites I have told him that it does not matter whether the links are from edu or gov;
however, he thought I am not good in SEO and he just finished the project. The thing which matters when you are placing a link is website worth and page rank only. Google treats all the links the same way, whether they are from gov edu twitter or facebook. The thing which matter is repute of the website, you might have seen few results when checking backlinks for a website they showed on first page.
I have some back links from reputable websites like v7n forums and blog catalog; they are shown on Google first page when you do a back link check. Now there is one thing that it might be useful to build on gov edu websites because their page rank is usually high. There is another issue which has been resolved now that creating links from wordpress, squidoo and other web 2.0 properties carries more weight.
The only thing, which is going to be considered, is page rank of the website, which will help you rank better. Thanks to Matt Cutts latest video which has cleared this thing, now you can show anyone that only reputes of the website matters in good rankings in search results.
There are so many people thinking about getting links from twitter and facebook, the big issue with facebook is that most of the groups and profiles are hidden and Google cannot grab the information from them. You won’t get any back link from them, Google do index links from facebook which are placed on those pages or groups which allows search engines and which are public.
Now you don’t need to worry about getting links from authority sites, if you plan a good SEO campaign to get back links from high page rank and old websites, it will help you rank high in search engines rather than specific links.