Apple will introduce new versions of iOS and OS X at its annual developer's conference.
Apple Starts Seeding Mac OS X 10.5.8 (9L14)
The new version of Mac OS X 10.5.8 offers the usual laundry list of fixes and changes to Leopard. Apple specifically cites 27 fixes across iDisk, iCal, Spotlight and more. It seems likely that this release will be the final update to 10.5 before we see the introduction of 10.6.
Mac OS X 10.6 has been announced to be due in September and is offering all current Leopard users an upgrade for only $29. Snow Leopard has always been described as primarily incorporating "under the hood" enhancements though we've seen reports of many more obvious changes.