That looks pretty good, but it appears to have no concept of users. In which case when you start replicating with somebody you end up with the same editable list of bookmarks. That may be what you want, but I'd quite like to be able to separate mine and theirs.
There are a few decentralized social networks around. I was considering the use of status.net as a base since it's got a load of the right features in there already (tagging, groups, federation, etc); though it may be best to just start from scratch using new and exciting technologies.
