How is IE7's tabbed browsing better? I've never really used IE7 outside of compatibility-checking. Most web devs will code to the w3c standards / Firefox and bugfix for IE, so the idea that IE7 has better site rendering is slightly absurd. For most shops I've been at, IE6 is a priority and IE7 an afterthought, so its rendering might actually be less accurate / more buggy than IE6. This is changing every day however (6 and 7 have ~the same market share, depending on where you look). Unless you're talking about an MS shop / Microsoft web apps, legacy / intranet sites, etc., which is valid but slightly beside the point.
FTR I *hate* Opera's tabbed browsing with a passion.