Richard MacManus carefully examines his personal publishing channels and notices a certain proliferation. I think this will be the short term trend for such services, as the Web works out what it wants. There's still a lot of task focused authoring, publishing and aggregation innovation to be had. Once users vote with their feet and focus on a small core set of services, then you'll start to see some consolidation. But that's a ways off.
The one common thread that seems to be running across these services is webfeed formats as data exchange mechanisms. Other than personal notebooks, all of the tools MacManus describes easily generate webfeeds. Even the private stuff, other than paper notebooks, could be made available through password protected URLs. While current aggregators are good at slurping and displaying webfeeds, tools like atomflow are going to be essential to stitching all this production together.