According to Apple Mac OS X 10.5 Leopard is delayed until October. This was posted on Apple Hot News (though no permalink unfortunately meaning it will likely disappear:
iPhone has already passed several of its required certification tests and is on schedule to ship in late June as planned. We can’t wait until customers get their hands (and fingers) on it and experience what a revolutionary and magical product it is. However, iPhone contains the most sophisticated software ever shipped on a mobile device, and finishing it on time has not come without a price — we had to borrow some key software engineering and QA resources from our Mac OS X team, and as a result we will not be able to release Leopard at our Worldwide Developers Conference in early June as planned. While Leopard’s features will be complete by then, we cannot deliver the quality release that we and our customers expect from us. We now plan to show our developers a near final version of Leopard at the conference, give them a beta copy to take home so they can do their final testing, and ship Leopard in October. We think it will be well worth the wait. Life often presents tradeoffs, and in this case we’re sure we’ve made the right ones. [Apr 12, 2007]
On the plus side I guess a few months of being feature complete would provide for a very stable release. I wonder if pre-orders will be taken prior to October? June seems slightly early to start. My guess would be Sept 1, with an announcement of when to expect pre-ordering in June.