The web is a wonderful place for humans but it's a less friendly place for machines. When we read a web page we bring along our own learning, mental models and opinions. The combination of what we read and what we know brings meaning. Machines are less bright.
Given a typical TV schedule page we can easily understand that Eastenders is on at 7:30 on the 15th May 2008. But computers can't parse text the way we can. If we want machines to be able to understand the web (and there are many reasons we might want to) we have to be more explicit about our meaning.
Which is where microformats come in. They're a relatively new technology that allow publishers to add semantic meaning to web pages. These might be events, contact details, personal relationships, geographic locations etc. With this additional machine friendly data you can add events from a web page directly to your calendar, contacts to your address book etc. In theory it's a great combination of a web for people and a web for machines. But it has some potential problems.
One potential problem is microformat's use of something called the abbreviation design pattern.
Basically, if you have a screen reader and have abbreviation expansion turned on, they'd like to hear from you.
This overloading of the abbreviation tag also has implications for people using abbr correctly. It's a nice inline way to help explain jargon, but if browsers and screen readers change the way they parse and present the content, we'll lose that functionality.
The BBC guys also have a very interesting post on 'Helping machines play with programmes'.