ya it was stable enough until one day it just bricked itself out of nowhere.
Also found this
"Mark Dowd and Tarjei Mandt, who described the iOS 6 kernel exploit, noted in a presentation in Kuala Lumpur this month that Apple has hardened the iOS kernel, provided better protection against memory or heap corruption errors, and improved stack overflow prevention. In addition, some APIs that had been used to execute exploits have been zeroed out, and Apple has further randomized address space layout randomization (ASLR) to make it more difficult to circumvent."
Most notably is the last sentence which talks about ASLR. (Address space layout randomization (ASLR) is a computer security technique involved in protection from buffer overflow attacks.) This was supposedly one of the issues of the ios 6 jailbreak.
Wikipedia:
"In many systems, 2^N can be in the thousands or millions; on modern 64-bit systems, these numbers typically reach the millions at least."
http://en.wikipedia.org/wiki/Address_space_layout_randomization
So I have a feeling that A7 chip has much greater capability to defer intrusion