The LA Weekly is one of the few publications that managed to get an interview in with Hayao Miyazaki while he was in California last month to promote Ponyo, and an interesting interview it is, covering some of Ponyo's source material, and the very future of Studio Ghibli itself.
A lot of reviewers, myself included, have noted that Ponyo is more of a return to true child-oriented films after titles like Princess Mononoke and Spirited Away, which were more geared towards adults. Miyazaki says it's due to his own empty nest that he can plunge into his own childhood-- and that many of the then-younger Ghibli staff now have young children. Apparently Fujimoto is lightly based on animation director Katsuya Kondo, who is having a lot of trouble handling his daughter.
As for his next project-- and yes, Miyazaki says he will just have to continue being an anime director, no declarations of retirement this time! --but he offers that Ghibli is going to have to find some new and younger directors, "because we'll disappear if we keep relying on old people."
Everything that Ghibli has put out in the last ten-- actually, in the last twelve --years has been directed by either Hayao Miyazaki or his Ghibli co-founder Isao Takahata, with two exceptions: Goro Miyazaki's ill-fated Tales from Earthsea (though the Miyazaki son is set to direct another Ghibli film for 2010) and Bokurano TV anime director Hiroyuki Morita's 2002 film The Cat Returns.
So it'll be interesting to see what other young directors Miyazaki and Takahata will try to pick up in order to carry on the Ghibli tradition of high-quality traditional animation.