I just installed Mozilla Firefox 3. Rather than all the excellent new features, the thing that really struck me was that the tabs were upside-down.
I wonder why they did it that way? I can see that the tabs have a relationship to the things above and below the tab area, but them being upside-down (and thus non-conventional) makes me stop and think about the tabs rather than doing what I was already doing.
Don’t get me wrong, I am not suggesting this is going to cause “real users” usability issues. Rather I think this is something that us in the usability design community will get deeply analytical about.