If Best Buy are to be believed, then The Legend of Zelda: Skyward Sword will be released in the US on September 25th 2011.
The release date shouldn't be taken as anything official though and it's likely just a estimated date from the retailer (which usually turn out to be false).
Nintendo will presumably be showcasing more of Skyward Sword at this years E3, held between June 7th - 9th. If any official release date is to be announced soon, it's expected to be announced at the event or more specifically, during Nintendo's Press Conference.