Gmail's mobile client for BlackBerry has been updated and you can now download version 2.0.5 at http://m.google.com/mail. One of the most important changes is that you can add the credentials for multiple accounts and switch between them without entering the password. There's also support for Google Apps accounts, which previously required a separate application.
Users from the PinStack forums report that the application lets you copy-paste text when composing messages, it saves more than one draft message and there's a new option to preload the archived messages.
Gmail's help center mentions that "the Gmail application will run in the background, periodically checking for new email. This uses data. If you do not want Gmail to run in the background, you must explicitly quit the program by going to Menu > Exit Gmail".