No, there's no significant ramp up. HTML5 introduces new elements that you can incorporate over time into the websites you work on. Old HTML will continue to be supported – Well most of it anyway. Some very old elements of HTML, such as blink, applet, frame and frameset, are designated as "obsolete" in HTML5. Browser manufacturers are encouraged to continue their support for obsolete elements to provide backward compatibility, but they are not required to.
At the simplest level there are new elements whose use is obvious — article, header, footer, aside, nav and section — to provide a finer level of semantic description of documents.
There are new elements for media — video and audio — which are tremendous improvements over the object, param and embed elements used with plugin technologies. These new media elements are as easy to use as the IMG tag.
There are new form input types that will verify user input automatically: "email", "url", "search", "number", plus additional attributes like "placeholder" and "required", that will reduce the amount of extra coding needed.
Most of the new features of HTML5 permit graceful fallback in non-compliant browsers and there are tools available to add support for new elements in legacy browsers. Google Chrome Frame, for instance, is a free plugin that gives IE the HTML5 capabilities of the Chrome browser. There's also an HTML5 shim that dynamically attaches new HTML5 elements to IE’s document object model (DOM) making HTML5 workable for IE7 and IE8 users.
Author: HTML Manual of Style