Facebook appears to be testing (with a far greater audience than I could), the current state of web conventions. A few years ago, few regular people knew that the logo on a website would link back to the homepage. Anecdotally, I have noticed more people using logos for that purpose in usability testing, but it’s very difficult to know what proportion of the general population that is.
Facebook, in the new design, has both a ‘home’ link as well as the logo:
My mouse was hovering over the logo, which displays a little ‘home’ icon when you do.
The really interesting thing is that the URL that you get from these otherwise identical links:
http://www.facebook.com/home.php?ref=logo (for the logo)
http://www.facebook.com/home.php?ref=home (for the home link)
They don’t make any difference to the page you get, but those variables will be recorded in the server logs, giving them a straight forward answer to:
How many people click the ‘home’ link compared to clicking the logo?
For many sites it is less obvious that the logo is the homepage, so this will be the best case scenario, I wonder if they will share the results?