PIxelGamerUK spotted that the US Sony Entertainment Network had Watch Dogs' release date down as June 30. Amazon.com also lists it as June 30.
There has been no official word from Ubisoft on the Watch Dogs release since its delay from the originally intended date in November. The June 30 date poses a couple of questions as it's a Monday and video games rarely sees releases on Mondays. Second it's the last day of Ubisoft's fiscal quarter, a date routinely used as placeholder.
Anyway, take it for what it is. A rumour at this point, but we suspect Ubisoft will be making an official announcement with regards to the release date sooner rather than alter.