Google have announced that they are discontinuing their Gmail App for BlackBerry, with support for the App being dropped in less than 10 days time.
Google recommends that users access their email though the browser, but there is a better way; use AstraSync to get full PUSH two way sync of Gmail, calendar and contacts to your BlackBerry.
Full details of how to configure AstraSync to access your Gmail, calendar and contacts on your BlackBerry can be found on the AstraSync Website
AstraSync, BlackBerry Gmail Sync
EDIT 2013-02-23:
It looks like Google have decided to leave BlackBerry and other smartphone users completely out in the cold ending support for the ActiveSync service on Gmail. More information can be found here: http://support.google.com/a/bin/answer.py?hl=en&answer=2716936&topic=27549&ctx=topic