The most official website for Death at a Funeral is the Sydney Kimmel Site which continues to report the following release date.

US theatrical release on 27 April 2007, distributed by MGM.

Unfortunately, the site does not update very frequently.

IMDb.com is reporting a release date of

Release dates for Death at a Funeral (2007)

However, IMDb's data isn't always reliable as users can add inaccurate information. I'm not sure why the Netherlands would see the movie one month earlier than the US, either. I suspect the information at IMDB is either incomplete or inaccurate. However, I wanted our readers to know the expeced date of US release may change.

Edit: sissicat, an administrator of the Italian forum, confirms that the date of US theatrical release is June 29, 2007. A member of her forum emailed the Italian distributor and confirmed the June release date for the US.