Some people have asked why we didn’t put tabs in IE sooner. Initially, we had some concerns around complexity and consistency… will it confuse users more than it benefits them? Is it confusing if IE has tabs, but other core parts of the Windows experience, like Windows Media Player or the shell, don’t have tabs? I think we made the wrong decision here initially, and we’re making the right one now. I’d like to ask you to post a comment with your favorite or most critical IE add-ins… we want to make sure IE7 works great with them.More details about IE7 at MSDN
Internet Explorer 7 will have tabs

A Microsoft employee today revealed Internet Explorer 7 will feature tabs: