From the UK’s Official Nintendo Magazine: “Buy Issue 10 of ONM. It’s on sale on 27 October. We’re not ones to encourage the wishing away of life, the summer and everything else, but this is pretty much bound to be the issue in which we review the Revolution launch line-up. Did the second hand on that clock just move backwards? Hurry up, October!”
While it’s possible this is their educated guess, after learning the Playstation 3 will launch worldwide in November. Since Nintendo did mention a year ago that they would launch before, but no later than their competition (Sony) and at the same time this is the Official Nintendo Magazine. Rest assured that you will know the launch dates and much more info on the morning of May 9th, at Nintendo’s pre-E3 press briefing.