The acquisition announcement is a an awkward moment, one of the high water marks in passive agressive writing. You have to convey the news in an upbeat way, but everyone knows that it means a few people will get rich, some people will lose jobs, or maybe the company just won't exist anymore. Express some gratitude to the users and/or employees, maybe talk about how "thrilled" you are. Many of these products simply don't exist anymore, or like mail client Sparrow are forever frozen in time, never to be updated again.
Music video director Jordan Fish, who made an amazing "choose your own adventure" video for Chairlift's "Met Before", put together a tumblr of splash pages of acquisition announcements into the tumblr "We've Been Acquired".
You can tell a lot about a company by the way it describes its acquisition.