This is a very short blog, but it appears that the GlobalNavigationNodes member on the PublishingWeb class has moved in SharePoint 2010.

http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.publishing.publishingweb.globalnavigationnodes(office.12).aspx

In SharePoint 2007, this was under Microsoft.SharePoint.Publishing.PublishingWeb.GlobalNavigationNodes

http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.publishing.navigation.portalnavigation.globalnavigationnodes.aspx

In SP2010, this has moved under Microsoft.SharePoint.Publishing.PublishingWeb.Navigation.PortalNavigation.GlobalNavigationNodes

This particular property is used to read a publishing site's navigation settings - I've used this to export site navigation as XML to accompany a site export.  Since site exports doesn't seem to include any customized site navigation information.  (It still doesn't in SP2010).