lucy24 - 8:28 pm on Jun 23, 2011 (gmt 0)
Some sites* start with a simple and voluntary "Try our new beta version!" in increasingly large type over the months. Final stage is where the beta becomes your primary address but you keep a link to the "classic" version for a while longer-- or even permanently, if the new version makes significant new demands on the user's hardware. If there are increased demands on the wetware, you have made a mistake.
* Unfortunately the only one I can think of by name is Perseus, which is not what you're looking for ;) --if only because that's the whole site, not just one area.