Not a biggy for me. I use Blend for XAML design. I think this is a good thing and that rolling Blend's features into VS makes sense. I tired of having to move between Blend and VS during development.
At least for now (and AFAIK there are no plans to change that) you'll have to continue switching. When they say "integrate with Visual Studio" they mean with the package, not with the IDE. It's still a separate program/tool.