Accelerators in Internet Explorer 8 help you quickly perform your everyday browsing tasks without navigating to other websites to get things done.
Simply highlight text from any webpage, and then click on the blue Accelerator icon that appears above your selection to obtain driving directions, translate and define words, email content to others, search with ease, and more. For example, with the "Map with Bing" Accelerator in Internet Explorer 8, you can get an in-place view of a map displayed directly on the page.
Check-out this blog post by Jon “Out-of-The” Box where he provides an excellent in-depth overview of the various options available for defining a great IE8 Accelerator for your web site.
Check it out!