Ok. Let's me explain.
What is Web 2.0
- Web 2.0 is mean a combination of the technology (like AJAX) allowing the customers to actually interact with the information.
Web2.0 is a like a social community on the internet. youtube, myspace, sqidoo, friendster, facebook, technorati, del.icio.us, digg, netscape, stumbleupon are all web2.0 services. Tha aim of web 2.0 to facilitate collaboration and sharing between users.

Many of these web 2.0 usually have high google PageRank. Today, web 2.0 is more easy to create backlinks to our website/blog.

For example youtube, if we want to make backlinks there, just sign up there and insert URL of our website/blogs at your profile. So, when someone comes to your profil, they will see your website information and they will go to your website. So, you can get traffic from there.

These method i use is to help me for building authority sites for long terms use.

Now, facebook is very popular site. Why not we just put URL of our website/blogs there. Take advantages from this site and other web 2.0.

But, that's not mean you should just create your backlinks at Web 2.0. You also need to create backlinks other site like forum, comment and others.