One of the new features in IE8 is called "web slices". Web slices let users subscribe to parts of a Web page and then get notified of updates directly in the IE8 favorites bar. This is great for pages where users often want to check for changes on a page. An obvious application for this is watching an auction on eBay.

It's up to the website owner to add code to their site to make web slices available. A library of known sites with web slices can be found at: http://www.ieaddons.com/en/webslices/

If you have your own web site and you want to enable slices for your site, there's a good tutorial on how to add markup to your site to enable web slices at MSDN: http://msdn.microsoft.com/en-us/library/cc956158(VS.85).aspx