Does anybody can explain to me what is the difference between social sites and directories? Because to me they are approximately the same thing except the fact that at a social site you must make an account in order to submit your site. So beside the fact that you have to make an account for posting a link and get some traffic one day or two what is the difference?? Why people are putting social sites as a very important part of SEO? Because from my point of view social site ~ directory ~ worthless for nowadays SEO...
Because Google has devalued links coming from directories and you receive little benefit in the way of traffic. They have been very public about telling webmasters to stay away from directories so I consider it good advice. Social sites, i.e. StumbleUpon can actually drive traffic to your site which is ultimately what most people want. Most social sites are nofollow but the more people visit and value your site, the more likely you will receive natural links which really what you want. I suspect there is some SEO value in Google for a nofollow link, especially if it contains keywords and not a competitive term. Many argue that Yahoo considers nofollow links even more. Thus, big difference overall
I will start with saying that google has 'NOT' devalued links from directories. Social sites are mostly used for direct traffic, branding and link baits. Most SB sites are nofollow. Another difference is that not many directories accept deep links.
Social sites is the fastest way to gather Direct live link, rather to submit in a lot of web directories.