Well, besides the integrated inbox and threaded conversations that we’re highlighted as new features of the iOS 4 mail program. Apparently, the Gmail integration also changed the default action of “trashing” an email. Nope, doesn’t delete it from your Gmail accounts, it archives it. Whoops!
It’s not nice to change the default action without telling anyone!
Read more about how to change it, if you want to, here at the Apple site.