According to Jared Spool from UIE, persistent global navigation isn't important to users:
"Maybe they'll click on the global navigation on the home page (however, probably not, if the page is well designed). Then they'll never click on it again, because, after all, they are now looking for local information - not global information"
"We've observed that it's almost always the case that if a user is clicking on global navigation, it's because they are completely lost."
"Having global navigation isn't a bad thing. It's just not something that should garner a lot of resources, as it's unlikely to be important in the user experience."
- The article Global Site Navigation: Not Worthwhile?
- October 21, 2005 - via Usernomics
See also: Research (93) Navigation (46)