A personal event network is like an OS for your personal cloud. You can install apps to customize it for your purpose, it can store and manage your personal data, and it provides generalized services through APIs that any app can take advantage of.
Everyone has a cloud strategy these days. Of course, when you hear about clouds, you hear questions like "Are we talking about IaaS, PaaS, or SaaS?" This assumes an enterprise-centric view of clouds that is belied by what Robert Scoble calls the game of games. Facebook, Google, and Apple are most selling clouds in various guises and see their cloud strategy as a key to their future.
The problems with these "personal clouds" is that they have no operating system. An operating system is what makes your personal computer personal. Without an OS, it would be a special purpose appliance that does specific things (like run an office suite) but not others (like play a game). There are certainly those who wish that was the norm, but for now, at least, we have general purpose computers that run a variety of applications and can be configured according to the dictates and wishes of their owners.
[An aside for those of you getting ready to comment: yes Facebook allows apps and is an app platform, but they are ancillary to the experience, not core. The core experience is still very much a Facebook-determined thing.]
The user-focused clouds we see today are special purpose. You can't customize them much or make them do something their builders didn't envision in the selection of applications that they offer.
In contrast a personal event network is like an OS for your personal cloud. You can install apps to customize it for your purpose, it can store and manage your personal data, and it provides generalized services through APIs that any app can take advantage of.