I absolutely hate the Design/Split/Source button bar whenever I am editing markup. It is especially annoying whenever I switch to full screen, because it still appears, even though it serves no purpose for me. Therefore, I opt to completely remove it, as you should do as well. I think this may also count as a minor performance tweak, as there is less processing that studio will have to do when switching to the html editor. Below is how to completely remove it:
Add a new DWORD entry in your registry at:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\VisualStudio\9.0\Packages\{1B437D20-F8FE-11D2-A6AE-00104BCC7269}
Name the DWORD DisableDesignView and set its value to 1.
Reload Visual Studio and the annoying bar is removed. You should note that this may also disable your CSS intellisense. but who needs that?