Sadly, Apple is amazingly good at keeping users from downgrading an iPhone. For some reason, a prior update (5.1.1) bricked my 3GS, and that's how I learned the hard way how firmly Apple had control of the upgrade/downgrad process. I find that annoying, as well as the fact that Apple "pushes" (figureatively and literally) updates on users, many of whom simply update immediately, without realizing there could be a downside. I've been amazed at how many non-techy iPhone using friends have complained to me about maps, and they wish they had never updated to iOS 6.
Anyway, I'm still using iOS 5 on my iPhone 4S, as I just feel too attached to my good old Google-based Map app (and the web version of Google Maps is really very different than the App version -- I tried it, thinking I would finally update my iPhone, but was really dissatisfied with the web version). I do know iOS 6 is superior in many ways, but for now, I am just that attached to my good old Map app.