Apart from the screenshots, everything was confirmed by Chris Wilson, IE platform architect at MIX'07.

http://arstechnica.com/news.ars/post/20070502-microsoft-drops-hints-about-internet-explorer-8.html
http://blogs.zdnet.com/microsoft/?p=416
http://internetexplorer8.net/

If Office 2007 has this new menu system, seems logical that MS will apply the same design for their other products. Doesn't look fake to me...