http://thirdblogfromthesun.com/2010/10/the-story-of-help-in-visual-studio-2010-part-3/

We’ve made three major changes to the Help Viewer in SP1. First, we’ve abandoned the browser-as-local-help-viewer and implemented a simple client application for offline help. The help window is no longer lost in the set of browser tabs you have open and the help application icon can be easily located in the taskbar. F1 Help re-uses the currently active tab instead of creating a parade of open tabs that must be manually managed. The help application can be sized and placed anywhere on your desktop and retains its size and placement across sessions. The navigation panel width is resizable and it can be placed to the right or the left of the content.

Second, with the flexibility we gain from building a client application, we’ve re-introduced many of the productivity/efficiency features found in Document Explorer. The viewer features four navigation tabs: a fully-expandable table of contents that can be explored without reloading the current topic, a keyword index, a Favorites and History tab, and a search results pane. The search results pane allows you to refine your search queries without losing your current topic context. In addition, context menus and shortcut keys allow you to access features quickly without excessive need for a mouse.

Finally, without the security restrictions of the browser, we’ve improved the ease with which you can manage local content. A direct link to the Help Library Manager is built into the viewer window. We provide improved guidance if you’ve never downloaded local documentation or if you press F1 on a topic for which local help is not installed.

http://msdn.microsoft.com/en-us/vstudio/gg288980.aspx