Okay, so I've read the Microsoft Hailstorm White Paper, and read a whole load of articles about it. It's a fascinating and complex concept. My executive summary is roughly as follows:

Taking all the services that people have on intranets, usually with Outlook, like contacts management, calendaring, appointments auto-added across calendars, expenses, the whole lot, and taking it to the internet, for the masses (with one interface the MSN Instant Messager). All remote calls are done using SOAP, all data in XML. Buzzword city. Information is kept on centralised servers, authentication performed using Microsoft Passport.

I like it. But: Okay although there are many ways to feed into the storage area, there's no way for me to swap the backend. There's no way I can build my own Hailstorm that would interoperate with the Microsoft version. And these are services that many people can and do offer already: Microsoft aren't providing any way for people to work together; they're duplicating online wallets, calendars and so on, the only advantage being that more people will use the same service (so it can be hooked into websites in confidence that people will be using it). Oh, and it provides lock-in for Windows. So I like it, but I'm concerned.