There are two new features that Microsoft is announcing the Beta1 version of Internet Explorer 8.  These two new features are Activities and WebSlices, as mentioned in the keynote. 

Activities

• XML installed to the browser using the OpenService Format
• There are a few simple components that make up an activity – Category, Context, Execute, and Preview
• Category – This is a way to group the different Activities you add – in this example, it is Maps
• Context – text that shows up in the context menu, context is typically “selection”, which will use the text that you have highlighted
• Execute – the actual URL that will be launched, with {selection} in curly brackets to dynamically pass the selection
• Preview – setting this will allow for a mouseover preview – action is a URL, requires parameters for size and selection

WebSlices

• Little purple button letting user know you can subscribe to the WebSlice
• An item is added to the favorites bar
• This can be eBay items, Facebook friends, Stumbleupon, NY Times most emailed articles, etc.
• WebSlices is based on hAtom Microformats
• These are implemented using style classes – some from hAtom (entity-title, entity-content), some are new (hslice)
• You must have a unique ID on an hslice
• Leverages and expands the Windows Feeds Platform shipped with IE7
• Also takes advantage of improved links bar – bold is updated, italics is expiring soon, and gray is expired
• Converts WebSlices into an Atom Feed
• Update schedule in the browser from once a day to every 15 minutes
• Use the TTL  class type to determine time-to-live that will be respected
• You can also define alternative feed URLs, and an end time
• The hover behaviors can be hidden to prevent hover behavior conflicts.  If you do this, it is easy to add a button that will add the WebSlice instead.  The same API can be used for links and feeds.
• If you need a username & password to get to the original content, the WebSlice dialog will ask for it to update the WebSlice
• Feeds should be used for lists of items instead of just a piece of page content

Conclusion

This is a preview of some of the new developer features in IE8.  There will be lots more to come, including new user-centric features.  Based on what I have seen, that should be very exciting stuff too!