User blog comment:Dopp/Technical Update: August 9, 2011/@comment-3080486-20110810114054/@comment-126761-20110810143532

There's no new requirement to use visual mode, but the layout update affects both modes. I know there's some concerns about it potentially being slower, which we're continuing to work on, but any effect while in source-only mode should be minimal. (To reiterate: this is not the end of our work on the editor!)