Originally Posted by tubemonkey
That's not a complete answer, since it didn't address the 50MB limit. Amazon's response just adds to the confusion and compounds it.
Here it is straight from the official "amazon kindle keyboard support" page:
An amazon policy change announced 2012 July 1 added this text:
The Experimental Web Browser is currently only available for some customers outside of the United States and may be limited to 50MB of browsing over 3G per month. This limit does not apply when customers are browsing over Wi-Fi.
So, it appears that the 50mb limit really DID go into effect on 2012 July 1, which tends to support the claims made in the first post of this thread.
More supporting information: