Just came across Tagsurf. Haven't wrapped my head around it yet but having registered and logged in (the registration process is made difficult by a barely legible capcha), it looks to be very powerful.
I guess one way to describe what I *think* this is about is del.icio.us URL tagging + annotation + access control + Flickr style goodies + customization + filtering/custom views + RSS for everything... for "topics".
Seems brand spanking new so there isn't much in it yet. Gonna play for a few days see where it goes.
Update 1:
So I'm using it to annotate stuff I find, be it news articles, blog entries, neat stuff... URLs basically - and you all can comment ("reply") to my annotations, or trackback to them from your weblog. It's del.icio.us on steroids, and so much more. I can trackback to whatever it is I'm writing about (if the source accepts incoming pings), you can use it as a comment system for your own blog if you wish, or as a blog in and of itslef. You can track topics, discussions on specific topics or specific URLs, tag everything system wide or just for yourself, select a copyright license for your notes...
LOTS of features... and amazingly, with a totally spartan UI, it is still quite usable; you just have to play with it to "get it".
Ohhh... community trust meters! :)
Update 2:
Here is a Bookmarklet for easily adding stuff to Tagsurf.
Duh, they have their own Bookmarklets already done:
