I just downloaded RC1 of IE8 to check it out. One of the first things that I have noticed is that a usability issue I was having regarding tab focus seems to have been fixed. I use Windows Live extensively was my mash-up of blogs and sites I like to keep track of. An anoying behaviour with IE7 tabs was that after clicking on a post in Windows Live it would load the article in a new tab, when I had finished readin the post I would close the tab to go back to Windows Live to find the next post I wanted to read. Well IE7 when you close a tab would give focus to the next tab on the right if there was one, which there usually was in my case, rather than Windows Live which was to the left. Well IE8 gives focus to the tab on the Left, Yeah!.
Another interesting feature is tab grouping, which visually is the tab that you clicked a link on and the tab containing the link being coloured the same, as above. Not sure if this will provide any value but interesting none the less.