While I am on the subject of next generation browsers, this is what I think of IE 7: bury it. As Microsoft mentioned countless times before IE 7 was announced, the dang thing has a list of legacy issues long enough to practically guarantee future problems.
Let it just rot and, instead, build a new browser that taps .NET 2.0's full potential. ActiveX? Leave it behind. Netscape Plugins compatibilty? AJAX? Piss on the whole stinking lot and move on to build a better canvas onto which developers can paint their picture on without twisting everywhich way like we have to do now to build even a crippled web application.
Microsoft should be doing more than just dicking around with silly ornaments like browser tabs.