IE7 has tabbed browsing
To be honest, I'm underwhelmed about IE7 having tabs but that's what people want, so that's what people get ;o)
Rest assured though, that there is far more cool stuff in IE7 than just tabbed browsing. Unfortunately, though, I'm not in a position to share details. We have to wait for the IE dev team to release information in its own time, and we also have to wait and see what makes it into the final cut - I, for one, remember how spamblocking was removed from OE5 thanks to a precipitous lawsuit by bluemountain.com.
Watch this space, and the IE team blog, for more info as it comes public.