Roger Black‘s notion of web 2.0 design:
The concept of web 2.0 design is to provide a set of tools and services to your user so that they can customize your website as they like to see it. It probably will be not more than 5% of the users that would do these customizations, but that would be worth it. After all, these are the people that love you.
You already see companies like Virb, Tumblr providing these kind of controls. Netvibes, Pageflakes and to some extent MSN.com has provided some kind of control on the blocks of content that you see on your home page.
And when it comes to Web 2.0 concepts of forums, discussions, comments, ratings, user generated content – giving your user controls on how they want to see all this data helps them dig into the data. Just the flexibility to see comments in a collapsible format or a stream of comments can be useful.