It depends on what you consider distributed vs. centralized. A blog that hosts its own commenting system has centralized everything onto its own server. By part

It depends on what you consider distributed vs. centralized. A blog that hosts its own commenting system has centralized everything onto its own server. By partitioning the content from the comments, you are decentralizing the various pieces that make up the site. To truly decentralize things you could open up a web hosting and commenting system to anybody who participates. A user's web browser connects to your DNS servers and, a la BitTorrent, requests seeds of third-party services which hold the content. The browser establishes a quorum of servers which have responded with an identical hash of the contents. The content may be static or it may consist of references to other pieces of content which is similarly distributed, so the browser should recursively go through each piece and gather them up in a similar manner. You end up with a much slower web implementation, but it becomes fully distributed.