According to the last bits of information available, Intel should officially unveil its now mobile Ivy Bridge CPUS on April 23rd. From that data, computer manufacturers will then be able to launch their new models. As April 23rd is on Monday, next day being Tuesday, Apple could then immediately release new MacBook Pro (15 and 17") as well as iMac.
Of course it will depend on the real availability of such chips, but we can also imagine that Apple will organize a Special Event for such release, especially is the design of MacBook or iMac have been modified.
