At the official IE 8 website you will find all the information you need. Some of the features are:
Activities
Activities are contextual services to quickly access a service from any webpage. Users typically copy and paste from one webpage to another. Internet Explorer 8 Activities make this common pattern easier to do.
An example of a "send" Activity is a user reads an interesting article and wants to blog about a portion of the article. The user can select a portion of the article and uses the blog Activity. This navigates to the user’s blog site with the selection already available in the edit field.
Activities are services that the user can install and manage. Users can install them from the Internet Explorer 8 Service Guide or through any website that advertises Activities.
WebSlices
WebSlices is a new feature for websites to connect to their users by subscribing to content directly within a webpage. WebSlices behave just like feeds where clients can subscribe to get updates and notify the user of changes.
Internet Explorer 8 Users can discover WebSlices within a webpage and add them to the Favorites bar, a dedicated row below the Address bar for easy access to links. Internet Explorer 8 subscribes to the webpage, detects changes in the WebSlice, and notifies the user of updates. Users can preview these updates directly from the Favorites bar and click-through to the website to get more information.
Favorites Bar
In Internet Explorer 7, the Links bar provided users with one-click access to their favorite sites. The Links bar has undergone a complete makeover for Internet Explorer 8. It has been renamed the Favorites bar to enable users to associate this bar as a place to put and easily access all their favorite web content such as links, feeds, WebSlices and even Word, Excel and PowerPoint documents.
A user can easily add a link to the Favorites bar by using the Add to Favorites button and selecting the Add to Favorites Bar option.
Automatic Crash Recovery
Automatic Crash Recovery (ACR) is a feature of WindowsInternet Explorer 8 that can help to prevent the loss of work and productivity in the unlikely event of the browser crashing or hanging. The ACR feature takes advantage of the Loosely-Coupled Internet Explorer feature to provide new crash recovery capabilities, such as tab recovery, which will minimize interruptions to users’ browsing sessions.
Improved Phishing Filter
Internet Explorer 7 introduced the Phishing Filter, a feature which helps warn users when they visit a Phishing site. Phishing sites spoof a trusted legitimate site, with the goal of stealing the user’s personal or financial information. For Internet Explorer 8, we are building on the success of the Phishing Filter with a more comprehensive feature called the "Safety Filter."
For IT administrators, new Group Policy options are available to remove the user-override option and fully block access to known unsafe sites.