I would hazard a guess that yes there is a rule. Its covered in the general rule of not talking about bypassing mechanisms .... whether such bypassing is circumventing software license keys, jailbreaking phones or otherwise.
You should also realise that jailbreaking is a double edged sword that has disadvantages, for example, you loose many of the inherent security mechanisms of iOS when you jailbreak it. You may also encounter bugs and glitches that you would never encounter under normal operating conditions.
Most technically savvy people consider the security risks of jailbreaking (plus the risk of "bricking" your phone) outweigh any purported benefits.
Apple are working hard on maps, and there are also countless other map apps you can run on a non-jailbroken phone (including Google, which I believe has made a comeback).
Last edited by mixture; 4th Feb 2013 at 14:37.