Think of a web 2.0 profile link similar to a forum profile backlink.
Web 2.0 profile's are links that are included in "about me" sections, they are normally higher PR and more authoritative then a forum profile backlink.
The Web 2.0 you are probably thinking about are blogs - That is where you go and create a blog and submit your article to that blog (think wordpress, blogger, hubpages, squidoo, etc.) with contextual backlinks.