Does the app notify you when authentication is attempted? The reason I still use SMS is that I will instantly get notified if someone has my password and attempts to access my account.
I believe Facebook used to do just the notification part with some optional security feature where you had to name each new computer you used. They have 2 factor now, of course.
The main improvement I can see you've made is that it's real-time enough that you should be able to jump on it straight away and do something rather than the batch processes I suspect spammers use.
There was a cunning|creepy trick used by Facebook I recall reading about not that long ago[1] that relied on Outlook autoloading bgsound attributes despite image loading settings, but I don't know of any comparable holes in gmail.
[1] http://pandodaily.com/2012/03/06/facebook-knows-when-you-ope...