The Inquirer claims here that the launch will be from April 23 to 24 in Tunisia. So this means that it will be about a month for the new ATI graphics cards if Inq is to be believed.
I dont think it will be launched in Tunisia - I expect some big city in EU or USA. I also think that date is correct - at least friend who work for major retailer in central europe told me to expect R600 BEFORE MAY. He also told me (this is speculation) that it will be hard launch - I hope its true because I´m going to buy new rig in may.