Jason Kottke and other smart folks have been writing a lot about extending the web to be the ultimate über-platform: In his latest illustration Kottke draws a picture of a centralized aggregation unit for personal information:
To put this another way, a distributed data storage system would take the place of a local storage system. [...] [Y]ou let Feedburner "listen" for new content from all those sources, transform/aggregate/filter it all, and publish it to your Web space; [...] Think of it like Unix...small pieces loosely joined. Each specific service handles what it's good at. Gmail for mail, iCal for calendars, TypePad for short bits of text, etc. Web client, desktop client, it doesn't much matter...whatever the user is most comfortable with.
The whole syndication/aggregation system is absolutely fine for topics like weblog posts, photos or news headlines. But when it comes to private mail or appointments, people need to be seriously concerned about their privacy: In the above scenario they not only commit an intimate part of their private life to services like GMail or Upcoming, but they also allow third parties to distribute the information in formats other than HTML.
This doesn't necessarily need to lead into security problems, but the potential is there: Imagine people having no clue how to aggregate their mail, appointments and photos themselfes - they will sign up for a public service offering aggregation. (I'll continue using aggregation due to the lack of a better term.) Ultimatively they'll also be forced to publish their passwords for GMail (private mail!), Upcoming (private appointments!), Flickr et al. to this service, so they can aggregate (duh!) the personal RSS/Atom-feeds.
Call me paranoid, but I don't like these thoughts. Anyway, we are still relatively far away from such services and even farther away from wide adoption. Thinking about privacy right now won't hurt, though.