Courtesy of GhibliWiki (the Nausicaa.net crew), the Japanese DVD and Blu-Ray release of the making-of documentary, "How Ponyo Was Born," is being delayed until December. The deluxe edition, "Ponyo Special DVD Box" is being delayed as well. "Circumstances in production" is the official reason given, which suggests a need to shore up supplies for the busy holiday season.
As far as I am aware, the standard DVD of Ponyo on a Cliff by the Sea will still be released in July (next week, in fact), and the Blu-Ray will appear in December.
These, of course, are all the Japanese releases. There is no official word on North American DVD or Blu-Ray for Ponyo. I would certainly hope to see something in time for Christmas; in fact, I am expecting it. The short theater-to-home window fits this perfectly, and was likely a factor in the movie's August release.