In my previous posts I've already written about disabling XAML Designer in Visual Studio 2010, but i find that way very bad, because in spite of we will see only XAML code, XAML designer would also try to render.
Much better and simple way is it to open your xaml with "open with" option and choose " xml editor" instead of "xml editor chooser" and then set it as default option. In this case XAML designer won't try to render and all those ugly lags will go away.