Adding Top Navigation Bar programatically

Scenario:
One of my friend asked me how to add a new item to Top Navigation Bar.

Solution:
You can write a feature receiver and using Object model can update the Top Navigation Bar.

Code:

SPWeb web = SPContext.Current.Web;
web.AllowUnsafeUpdates = true;
if (!web.Navigation.UseShared)
{
  SPNavigationNodeCollection topNavigationNodes = web.Navigation.TopNavigationBar;

 // You can also edit the Quick Launch the same way
 //SPNavigationNodeCollection topNavigationNodes = web.Navigation.QuickLaunch;

  SPNavigationNode objItem = new SPNavigationNode("MyWorkspace", "default.aspx", false);
  topNavigationNodes.AddAsFirst(objItem);
}
web.Update();
web.AllowUnsafeUpdates = false; 

Errors:
If you try to put have a absolute url , you might get an error like this
Cannot open "/http://localhost/default.aspx": no such file or folder.

Also if you miss the check for the Shared Navigation , then you will get the following error
The top link bar can only be edited for a Web site with unique navigation.