"What, in your (and others) opinion, is the difference (if any) between the "online desktop" (A) (I'm thinking Netvibes and the like) and the "Personal Content Network" (B)."
Actually I'm seeing a lot of crossover and cross-pollination in the market segments I'm tracking these days. The Web Office theme I'm exploring over on my ZDNet blog is very closely aligned to the WebOS (i.e. web-based OS services) market. Goowy is an example of a product that is both an office suite and an OS/desktop type application. I also noted a few posts ago that PeopleFeeds, 43Things and Suprglu could be classified as anything from a Content Management system, to a Social Networking Service or an RSS Reader.
Another example: the increasingly hard-to-tell difference between a modern RSS Reader and a Personalized News service like Tech.memeorandum. RSS Readers like Rojo and the Newsgator family are adding more filtering and social recommendation functionality - taking their cue from successful services like Digg and Memeorandum. Meanwhile the likes of Tailrank and Megite are attempting to make their News aggregators increasingly personalized (like an RSS Reader).
So there is a lot of cross-pollination going on, which gives industry analysts like me something to chew on! ;-)
But back to Mike's specific question: what's the difference between Ajax Homepages (e.g. Netvibes, Pageflakes, Live.com) and Microcontent Aggregators (e.g. Peoplefeeds, Suprglu)? Peter Cooper followed up with this comment:
"Mike: The primary difference from my POV is that you don't really share entire Netvibes pages, but Superglu is something that other people can look at and use rather than just you."
I'd add that Ajax Homepages are designed to be a home for your external content sources and web services (aka widgets, gadgets, modules -- whatever you want to call them). So an Ajax Homepage like Netvibes or Pageflakes is more focused on being a central place to store your favourite content (news, RSS feeds, etc), plus a place to access all of your web apps and personalized services (like for example access to your Writely account, or your tv schedule -- i.e. much more than just the weather and clock apps you mostly see today).
The Personal Content Network services (to use Dick Costolo's great phrase) are much more about organizing the content you created - and as Peter noted, making it easier for other people to subscribe to and/or filter your content.
But we're certainly seeing a lot of interbreeding of functionality and features between web 2.0 market segments, which is an encouraging sign that developers and startups are paying attention to the landscape and trying new things in order to evolve.
Pollination pic: libraryman